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Writing a Literature Review

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A literature review is a document or section of a document that collects key sources on a topic and discusses those sources in conversation with each other (also called synthesis ). The lit review is an important genre in many disciplines, not just literature (i.e., the study of works of literature such as novels and plays). When we say “literature review” or refer to “the literature,” we are talking about the research ( scholarship ) in a given field. You will often see the terms “the research,” “the scholarship,” and “the literature” used mostly interchangeably.

Where, when, and why would I write a lit review?

There are a number of different situations where you might write a literature review, each with slightly different expectations; different disciplines, too, have field-specific expectations for what a literature review is and does. For instance, in the humanities, authors might include more overt argumentation and interpretation of source material in their literature reviews, whereas in the sciences, authors are more likely to report study designs and results in their literature reviews; these differences reflect these disciplines’ purposes and conventions in scholarship. You should always look at examples from your own discipline and talk to professors or mentors in your field to be sure you understand your discipline’s conventions, for literature reviews as well as for any other genre.

A literature review can be a part of a research paper or scholarly article, usually falling after the introduction and before the research methods sections. In these cases, the lit review just needs to cover scholarship that is important to the issue you are writing about; sometimes it will also cover key sources that informed your research methodology.

Lit reviews can also be standalone pieces, either as assignments in a class or as publications. In a class, a lit review may be assigned to help students familiarize themselves with a topic and with scholarship in their field, get an idea of the other researchers working on the topic they’re interested in, find gaps in existing research in order to propose new projects, and/or develop a theoretical framework and methodology for later research. As a publication, a lit review usually is meant to help make other scholars’ lives easier by collecting and summarizing, synthesizing, and analyzing existing research on a topic. This can be especially helpful for students or scholars getting into a new research area, or for directing an entire community of scholars toward questions that have not yet been answered.

What are the parts of a lit review?

Most lit reviews use a basic introduction-body-conclusion structure; if your lit review is part of a larger paper, the introduction and conclusion pieces may be just a few sentences while you focus most of your attention on the body. If your lit review is a standalone piece, the introduction and conclusion take up more space and give you a place to discuss your goals, research methods, and conclusions separately from where you discuss the literature itself.

Introduction:

• An introductory paragraph that explains what your working topic and thesis is
• A forecast of key topics or texts that will appear in the review
• Potentially, a description of how you found sources and how you analyzed them for inclusion and discussion in the review (more often found in published, standalone literature reviews than in lit review sections in an article or research paper)
• Summarize and synthesize: Give an overview of the main points of each source and combine them into a coherent whole
• Analyze and interpret: Don’t just paraphrase other researchers – add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
• Critically Evaluate: Mention the strengths and weaknesses of your sources
• Write in well-structured paragraphs: Use transition words and topic sentence to draw connections, comparisons, and contrasts.

Conclusion:

• Summarize the key findings you have taken from the literature and emphasize their significance
• Connect it back to your primary research question

How should I organize my lit review?

Lit reviews can take many different organizational patterns depending on what you are trying to accomplish with the review. Here are some examples:

• Chronological : The simplest approach is to trace the development of the topic over time, which helps familiarize the audience with the topic (for instance if you are introducing something that is not commonly known in your field). If you choose this strategy, be careful to avoid simply listing and summarizing sources in order. Try to analyze the patterns, turning points, and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred (as mentioned previously, this may not be appropriate in your discipline — check with a teacher or mentor if you’re unsure).
• Thematic : If you have found some recurring central themes that you will continue working with throughout your piece, you can organize your literature review into subsections that address different aspects of the topic. For example, if you are reviewing literature about women and religion, key themes can include the role of women in churches and the religious attitude towards women.
• Qualitative versus quantitative research
• Empirical versus theoretical scholarship
• Divide the research by sociological, historical, or cultural sources
• Theoretical : In many humanities articles, the literature review is the foundation for the theoretical framework. You can use it to discuss various theories, models, and definitions of key concepts. You can argue for the relevance of a specific theoretical approach or combine various theorical concepts to create a framework for your research.

What are some strategies or tips I can use while writing my lit review?

Any lit review is only as good as the research it discusses; make sure your sources are well-chosen and your research is thorough. Don’t be afraid to do more research if you discover a new thread as you’re writing. More info on the research process is available in our "Conducting Research" resources .

As you’re doing your research, create an annotated bibliography ( see our page on the this type of document ). Much of the information used in an annotated bibliography can be used also in a literature review, so you’ll be not only partially drafting your lit review as you research, but also developing your sense of the larger conversation going on among scholars, professionals, and any other stakeholders in your topic.

Usually you will need to synthesize research rather than just summarizing it. This means drawing connections between sources to create a picture of the scholarly conversation on a topic over time. Many student writers struggle to synthesize because they feel they don’t have anything to add to the scholars they are citing; here are some strategies to help you:

• It often helps to remember that the point of these kinds of syntheses is to show your readers how you understand your research, to help them read the rest of your paper.
• Writing teachers often say synthesis is like hosting a dinner party: imagine all your sources are together in a room, discussing your topic. What are they saying to each other?
• Look at the in-text citations in each paragraph. Are you citing just one source for each paragraph? This usually indicates summary only. When you have multiple sources cited in a paragraph, you are more likely to be synthesizing them (not always, but often
• Read more about synthesis here.

The most interesting literature reviews are often written as arguments (again, as mentioned at the beginning of the page, this is discipline-specific and doesn’t work for all situations). Often, the literature review is where you can establish your research as filling a particular gap or as relevant in a particular way. You have some chance to do this in your introduction in an article, but the literature review section gives a more extended opportunity to establish the conversation in the way you would like your readers to see it. You can choose the intellectual lineage you would like to be part of and whose definitions matter most to your thinking (mostly humanities-specific, but this goes for sciences as well). In addressing these points, you argue for your place in the conversation, which tends to make the lit review more compelling than a simple reporting of other sources.

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• How to Write a Literature Review | Guide, Examples, & Templates

How to Write a Literature Review | Guide, Examples, & Templates

Published on January 2, 2023 by Shona McCombes . Revised on September 11, 2023.

What is a literature review? A literature review is a survey of scholarly sources on a specific topic. It provides an overview of current knowledge, allowing you to identify relevant theories, methods, and gaps in the existing research that you can later apply to your paper, thesis, or dissertation topic .

There are five key steps to writing a literature review:

• Search for relevant literature
• Evaluate sources
• Identify themes, debates, and gaps
• Outline the structure
• Write your literature review

A good literature review doesn’t just summarize sources—it analyzes, synthesizes , and critically evaluates to give a clear picture of the state of knowledge on the subject.

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Table of contents

What is the purpose of a literature review, examples of literature reviews, step 1 – search for relevant literature, step 2 – evaluate and select sources, step 3 – identify themes, debates, and gaps, step 4 – outline your literature review’s structure, step 5 – write your literature review, free lecture slides, other interesting articles, frequently asked questions, introduction.

• Quick Run-through
• Step 1 & 2

When you write a thesis , dissertation , or research paper , you will likely have to conduct a literature review to situate your research within existing knowledge. The literature review gives you a chance to:

• Demonstrate your familiarity with the topic and its scholarly context
• Develop a theoretical framework and methodology for your research
• Position your work in relation to other researchers and theorists
• Show how your research addresses a gap or contributes to a debate
• Evaluate the current state of research and demonstrate your knowledge of the scholarly debates around your topic.

Writing literature reviews is a particularly important skill if you want to apply for graduate school or pursue a career in research. We’ve written a step-by-step guide that you can follow below.

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Writing literature reviews can be quite challenging! A good starting point could be to look at some examples, depending on what kind of literature review you’d like to write.

• Example literature review #1: “Why Do People Migrate? A Review of the Theoretical Literature” ( Theoretical literature review about the development of economic migration theory from the 1950s to today.)
• Example literature review #2: “Literature review as a research methodology: An overview and guidelines” ( Methodological literature review about interdisciplinary knowledge acquisition and production.)
• Example literature review #3: “The Use of Technology in English Language Learning: A Literature Review” ( Thematic literature review about the effects of technology on language acquisition.)
• Example literature review #4: “Learners’ Listening Comprehension Difficulties in English Language Learning: A Literature Review” ( Chronological literature review about how the concept of listening skills has changed over time.)

You can also check out our templates with literature review examples and sample outlines at the links below.

Download Word doc Download Google doc

Before you begin searching for literature, you need a clearly defined topic .

If you are writing the literature review section of a dissertation or research paper, you will search for literature related to your research problem and questions .

Make a list of keywords

Start by creating a list of keywords related to your research question. Include each of the key concepts or variables you’re interested in, and list any synonyms and related terms. You can add to this list as you discover new keywords in the process of your literature search.

• Social media, Facebook, Instagram, Twitter, Snapchat, TikTok
• Body image, self-perception, self-esteem, mental health
• Generation Z, teenagers, adolescents, youth

Search for relevant sources

Use your keywords to begin searching for sources. Some useful databases to search for journals and articles include:

• Your university’s library catalogue
• Google Scholar
• Project Muse (humanities and social sciences)
• Medline (life sciences and biomedicine)
• EconLit (economics)
• Inspec (physics, engineering and computer science)

You can also use boolean operators to help narrow down your search.

Make sure to read the abstract to find out whether an article is relevant to your question. When you find a useful book or article, you can check the bibliography to find other relevant sources.

You likely won’t be able to read absolutely everything that has been written on your topic, so it will be necessary to evaluate which sources are most relevant to your research question.

For each publication, ask yourself:

• What question or problem is the author addressing?
• What are the key concepts and how are they defined?
• What are the key theories, models, and methods?
• Does the research use established frameworks or take an innovative approach?
• What are the results and conclusions of the study?
• How does the publication relate to other literature in the field? Does it confirm, add to, or challenge established knowledge?
• What are the strengths and weaknesses of the research?

Make sure the sources you use are credible , and make sure you read any landmark studies and major theories in your field of research.

You can use our template to summarize and evaluate sources you’re thinking about using. Click on either button below to download.

Take notes and cite your sources

As you read, you should also begin the writing process. Take notes that you can later incorporate into the text of your literature review.

It is important to keep track of your sources with citations to avoid plagiarism . It can be helpful to make an annotated bibliography , where you compile full citation information and write a paragraph of summary and analysis for each source. This helps you remember what you read and saves time later in the process.

To begin organizing your literature review’s argument and structure, be sure you understand the connections and relationships between the sources you’ve read. Based on your reading and notes, you can look for:

• Trends and patterns (in theory, method or results): do certain approaches become more or less popular over time?
• Themes: what questions or concepts recur across the literature?
• Debates, conflicts and contradictions: where do sources disagree?
• Pivotal publications: are there any influential theories or studies that changed the direction of the field?
• Gaps: what is missing from the literature? Are there weaknesses that need to be addressed?

This step will help you work out the structure of your literature review and (if applicable) show how your own research will contribute to existing knowledge.

• Most research has focused on young women.
• There is an increasing interest in the visual aspects of social media.
• But there is still a lack of robust research on highly visual platforms like Instagram and Snapchat—this is a gap that you could address in your own research.

There are various approaches to organizing the body of a literature review. Depending on the length of your literature review, you can combine several of these strategies (for example, your overall structure might be thematic, but each theme is discussed chronologically).

Chronological

The simplest approach is to trace the development of the topic over time. However, if you choose this strategy, be careful to avoid simply listing and summarizing sources in order.

Try to analyze patterns, turning points and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred.

If you have found some recurring central themes, you can organize your literature review into subsections that address different aspects of the topic.

For example, if you are reviewing literature about inequalities in migrant health outcomes, key themes might include healthcare policy, language barriers, cultural attitudes, legal status, and economic access.

Methodological

If you draw your sources from different disciplines or fields that use a variety of research methods , you might want to compare the results and conclusions that emerge from different approaches. For example:

• Look at what results have emerged in qualitative versus quantitative research
• Discuss how the topic has been approached by empirical versus theoretical scholarship
• Divide the literature into sociological, historical, and cultural sources

Theoretical

A literature review is often the foundation for a theoretical framework . You can use it to discuss various theories, models, and definitions of key concepts.

You might argue for the relevance of a specific theoretical approach, or combine various theoretical concepts to create a framework for your research.

Like any other academic text , your literature review should have an introduction , a main body, and a conclusion . What you include in each depends on the objective of your literature review.

The introduction should clearly establish the focus and purpose of the literature review.

Depending on the length of your literature review, you might want to divide the body into subsections. You can use a subheading for each theme, time period, or methodological approach.

As you write, you can follow these tips:

• Summarize and synthesize: give an overview of the main points of each source and combine them into a coherent whole
• Analyze and interpret: don’t just paraphrase other researchers — add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
• Critically evaluate: mention the strengths and weaknesses of your sources
• Write in well-structured paragraphs: use transition words and topic sentences to draw connections, comparisons and contrasts

In the conclusion, you should summarize the key findings you have taken from the literature and emphasize their significance.

When you’ve finished writing and revising your literature review, don’t forget to proofread thoroughly before submitting. Not a language expert? Check out Scribbr’s professional proofreading services !

This article has been adapted into lecture slides that you can use to teach your students about writing a literature review.

Scribbr slides are free to use, customize, and distribute for educational purposes.

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If you want to know more about the research process , methodology , research bias , or statistics , make sure to check out some of our other articles with explanations and examples.

• Sampling methods
• Simple random sampling
• Stratified sampling
• Cluster sampling
• Likert scales
• Reproducibility

 Statistics

• Null hypothesis
• Statistical power
• Probability distribution
• Effect size
• Poisson distribution

Research bias

• Optimism bias
• Cognitive bias
• Implicit bias
• Hawthorne effect
• Anchoring bias
• Explicit bias

A literature review is a survey of scholarly sources (such as books, journal articles, and theses) related to a specific topic or research question .

It is often written as part of a thesis, dissertation , or research paper , in order to situate your work in relation to existing knowledge.

There are several reasons to conduct a literature review at the beginning of a research project:

• To familiarize yourself with the current state of knowledge on your topic
• To ensure that you’re not just repeating what others have already done
• To identify gaps in knowledge and unresolved problems that your research can address
• To develop your theoretical framework and methodology
• To provide an overview of the key findings and debates on the topic

Writing the literature review shows your reader how your work relates to existing research and what new insights it will contribute.

The literature review usually comes near the beginning of your thesis or dissertation . After the introduction , it grounds your research in a scholarly field and leads directly to your theoretical framework or methodology .

A literature review is a survey of credible sources on a topic, often used in dissertations , theses, and research papers . Literature reviews give an overview of knowledge on a subject, helping you identify relevant theories and methods, as well as gaps in existing research. Literature reviews are set up similarly to other  academic texts , with an introduction , a main body, and a conclusion .

An  annotated bibliography is a list of  source references that has a short description (called an annotation ) for each of the sources. It is often assigned as part of the research process for a  paper .  

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• UConn Library
• Literature Review: The What, Why and How-to Guide
• Introduction

Literature Review: The What, Why and How-to Guide — Introduction

• Getting Started
• How to Pick a Topic
• Strategies to Find Sources
• Evaluating Sources & Lit. Reviews
• Tips for Writing Literature Reviews
• Writing Literature Review: Useful Sites
• Citation Resources
• Other Academic Writings

What are Literature Reviews?

So, what is a literature review? "A literature review is an account of what has been published on a topic by accredited scholars and researchers. In writing the literature review, your purpose is to convey to your reader what knowledge and ideas have been established on a topic, and what their strengths and weaknesses are. As a piece of writing, the literature review must be defined by a guiding concept (e.g., your research objective, the problem or issue you are discussing, or your argumentative thesis). It is not just a descriptive list of the material available, or a set of summaries." Taylor, D.  The literature review: A few tips on conducting it . University of Toronto Health Sciences Writing Centre.

Goals of Literature Reviews

What are the goals of creating a Literature Review?  A literature could be written to accomplish different aims:

• To develop a theory or evaluate an existing theory
• To summarize the historical or existing state of a research topic
• Identify a problem in a field of research 

Baumeister, R. F., & Leary, M. R. (1997). Writing narrative literature reviews .  Review of General Psychology , 1 (3), 311-320.

What kinds of sources require a Literature Review?

• A research paper assigned in a course
• A thesis or dissertation
• A grant proposal
• An article intended for publication in a journal

All these instances require you to collect what has been written about your research topic so that you can demonstrate how your own research sheds new light on the topic.

Types of Literature Reviews

What kinds of literature reviews are written?

Narrative review: The purpose of this type of review is to describe the current state of the research on a specific topic/research and to offer a critical analysis of the literature reviewed. Studies are grouped by research/theoretical categories, and themes and trends, strengths and weakness, and gaps are identified. The review ends with a conclusion section which summarizes the findings regarding the state of the research of the specific study, the gaps identify and if applicable, explains how the author's research will address gaps identify in the review and expand the knowledge on the topic reviewed.

• Example : Predictors and Outcomes of U.S. Quality Maternity Leave: A Review and Conceptual Framework:  10.1177/08948453211037398  

Systematic review : "The authors of a systematic review use a specific procedure to search the research literature, select the studies to include in their review, and critically evaluate the studies they find." (p. 139). Nelson, L. K. (2013). Research in Communication Sciences and Disorders . Plural Publishing.

• Example : The effect of leave policies on increasing fertility: a systematic review:  10.1057/s41599-022-01270-w

Meta-analysis : "Meta-analysis is a method of reviewing research findings in a quantitative fashion by transforming the data from individual studies into what is called an effect size and then pooling and analyzing this information. The basic goal in meta-analysis is to explain why different outcomes have occurred in different studies." (p. 197). Roberts, M. C., & Ilardi, S. S. (2003). Handbook of Research Methods in Clinical Psychology . Blackwell Publishing.

• Example : Employment Instability and Fertility in Europe: A Meta-Analysis:  10.1215/00703370-9164737

Meta-synthesis : "Qualitative meta-synthesis is a type of qualitative study that uses as data the findings from other qualitative studies linked by the same or related topic." (p.312). Zimmer, L. (2006). Qualitative meta-synthesis: A question of dialoguing with texts .  Journal of Advanced Nursing , 53 (3), 311-318.

• Example : Women’s perspectives on career successes and barriers: A qualitative meta-synthesis:  10.1177/05390184221113735

Literature Reviews in the Health Sciences

• UConn Health subject guide on systematic reviews Explanation of the different review types used in health sciences literature as well as tools to help you find the right review type
• << Previous: Getting Started
• Next: How to Pick a Topic >>
• Last Updated: Sep 21, 2022 2:16 PM
• URL: https://guides.lib.uconn.edu/literaturereview

Literature reviews as independent studies: guidelines for academic practice

• Original Paper
• Open access
• Published: 14 October 2022
• Volume 16 , pages 2577–2595, ( 2022 )

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• Sascha Kraus   ORCID: orcid.org/0000-0003-4886-7482 1 , 2 ,
• Matthias Breier 3 ,
• Weng Marc Lim 4 , 8 , 22 ,
• Marina Dabić 5 , 6 ,
• Satish Kumar 7 , 8 ,
• Dominik Kanbach 9 , 10 ,
• Debmalya Mukherjee 11 ,
• Vincenzo Corvello 12 ,
• Juan Piñeiro-Chousa 13 ,
• Eric Liguori 14 ,
• Daniel Palacios-Marqués 15 ,
• Francesco Schiavone 16 , 17 ,
• Alberto Ferraris 18 , 21 ,
• Cristina Fernandes 19 , 20 &
• João J. Ferreira 19  

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Review articles or literature reviews are a critical part of scientific research. While numerous guides on literature reviews exist, these are often limited to the philosophy of review procedures, protocols, and nomenclatures, triggering non-parsimonious reporting and confusion due to overlapping similarities. To address the aforementioned limitations, we adopt a pragmatic approach to demystify and shape the academic practice of conducting literature reviews. We concentrate on the types, focuses, considerations, methods, and contributions of literature reviews as independent, standalone studies. As such, our article serves as an overview that scholars can rely upon to navigate the fundamental elements of literature reviews as standalone and independent studies, without getting entangled in the complexities of review procedures, protocols, and nomenclatures.

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1 Introduction

A literature review – or a review article – is “a study that analyzes and synthesizes an existing body of literature by identifying, challenging, and advancing the building blocks of a theory through an examination of a body (or several bodies) of prior work (Post et al. 2020 , p. 352). Literature reviews as standalone pieces of work may allow researchers to enhance their understanding of prior work in their field, enabling them to more easily identify gaps in the body of literature and potential avenues for future research. More importantly, review articles may challenge established assumptions and norms of a given field or topic, recognize critical problems and factual errors, and stimulate future scientific conversations around that topic. Literature reviews Footnote 1 come in many different formats and purposes:

Some review articles conduct a critical evaluation of the literature, whereas others elect to adopt a more exploratory and descriptive approach.

Some reviews examine data, methodologies, and findings, whereas others look at constructs, themes, and theories.

Some reviews provide summaries by holistically synthesizing the existing research on a topic, whereas others adopt an integrative approach by assessing related and interdisciplinary work.

The number of review articles published as independent or standalone studies has been increasing over time. According to Scopus (i.e., search database ), reviews (i.e., document type ) were first published in journals (i.e., source type ) as independent studies in 1945, and they subsequently appeared in three digits yearly from the late 1980s to the late 1990s, four digits yearly from the early 2000s to the late 2010s, and five digits in the year 2021 (Fig.  1 ). This increase is indicative that reviewers and editors in business and management research alike see value and purpose in review articles to such a level that they are now commonly accepted as independent, standalone studies. This development is also reflected in the fact that some academic journals exclusively publish review articles (e.g., the Academy of Management Annals , or the  International Journal of Management Reviews ), and journals publishing in various fields often have special issues dedicated to literature reviews on certain topic areas (e.g., the Journal of Management and the Journal of International Business Studies ).

Full-year publication trend of review articles on Scopus (1945–2021)

One of the most important prerequisites of a high-quality review article is that the work follows an established methodology, systematically selects and analyzes articles, and periodically covers the field to identify latest developments (Snyder 2019 ). Additionally, it needs to be reproducible, well-evidenced, and transparent, resulting in a sample inclusive of all relevant and appropriate studies (Gusenbauer and Haddaway 2020; Hansen et al. 2021 ). This observation is in line with Palmatier et al. ( 2018 ), who state that review articles provide an important synthesis of findings and perspectives in a given body of knowledge. Snyder ( 2019 ) also reaffirmed this rationale, pointing out that review articles have the power to answer research questions beyond that which can be achieved in a single study. Ultimately, readers of review articles stand to gain a one-stop, state-of-the-art synthesis (Lim et al. 2022a ; Popli et al. 2022) that encapsulates critical insights through the process of re-interpreting, re-organizing, and re-connecting a body knowledge (Fan et al. 2022 ).

There are many reasons to conduct review articles. Kraus et al. ( 2020 ) explicitly mention the benefits of conducting systematic reviews by declaring that they often represent the first step in the context of larger research projects, such as doctoral dissertations. When carrying out work of this kind, it is important that a holistic overview of the current state of literature is achieved and embedded into a proper synthesis. This allows researchers to pinpoint relevant research gaps and adequately fit future conceptual or empirical studies into the state of the academic discussion (Kraus et al., 2021 ). A review article as an independent or standalone study is a viable option for any academic – especially young scholars, such as doctoral candidates – who wishes to delve into a specific topic for which a (recent) review article is not available.

The process of conducting a review article can be challenging, especially for novice scholars (Boell and Cecez-Kecmanovic 2015 ). Therefore, it is not surprising that numerous guides have been written in an attempt to improve the quality of review studies and support emerging scholars in their endeavors to have their work published. These guides for conducting review articles span a variety of academic fields, such as engineering education (Borrego et al. 2014 ), health sciences (Cajal et al. 2020 ), psychology (Laher and Hassem 2020 ), supply chain management (Durach et al. 2017 ), or business and entrepreneurship (Kraus et al. 2020 ; Tranfield et al. 2003 ) – the latter were among the first scholars to recognize the need to educate business/management scholars on the roles of review studies in assembling, ascertaining, and assessing the intellectual territory of a specific knowledge domain. Furthermore, they shed light on the stages (i.e., planning the review, conducting the review, reporting, and dissemination) and phases (i.e., identifying the need for a review, preparation of a proposal for a review, development of a review protocol, identification of research, selection of studies, study quality assessment, data extraction and monitoring progress, data synthesis, the report and recommendations, and getting evidence into practice) of conducting a systematic review. Other scholars have either adapted and/or developed new procedures (Kraus et al. 2020 ; Snyder 2019 ) or established review protocols such as the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flow diagram (Moher et al. 2015 ). The latter provides a checklist that improves transparency and reproducibility, thus reducing questionable research practices. The declarative and procedural knowledge of a checklist allows users to derive value from (and, in some cases, produce) methodological literature reviews.

Two distinct and critical gaps or issues provide impetus for our article. First, while the endeavors of the named scholars are undoubtedly valuable contributions, they often encourage other scholars to explain the methodology of their review studies in a non-parsimonious way ( 1st issue ). This can become problematic if this information distracts and deprives scholars from providing richer review findings, particularly in instances in which publication outlets impose a strict page and/or word limit. More often than not, the early parts (i.e., stages/phases, such as needs, aims, and scope) of these procedures or protocols are explained in the introduction, but they tend to be reiterated in the methodology section due to the prescription of these procedures or protocols. Other parts of these procedures or protocols could also be reported more parsimoniously, for example, by filtering out documents, given that scientific databases (such as Scopus or Web of Science ) have since been upgraded to allow scholars to select and implement filtering criteria when conducting a search (i.e., criterion-by-criterion filtering may no longer be necessary). More often than not, the procedures or protocols of review studies can be signposted (e.g., bracket labeling) and disclosed in a sharp and succinct manner while maintaining transparency and replicability.

Other guides have been written to introduce review nomenclatures (i.e., names/naming) and their equivalent philosophical underpinnings. Palmatier et al. ( 2018 ) introduced three clearly but broadly defined nomenclatures of literature reviews as independent studies: domain-based reviews, theory-based reviews, and method-based reviews. However, such review nomenclatures can be confusing due to their overlapping similarities ( 2nd issue ). For example, Lim et al. ( 2022a ) highlighted their observation that the review nomenclatures associated with domain-based reviews could also be used for theory-based and method-based reviews.

The two aforementioned issues – i.e., the lack of a parsimonious understanding and the reporting of the review methodology , and the confusion emerging from review nomenclatures – are inarguably the unintended outcomes of diving into an advanced (i.e., higher level) understanding of literature review procedures, protocols, and nomenclatures from a philosophical perspective (i.e., underpinnings) without a foundational (i.e., basic level) understanding of the fundamental (i.e., core) elements of literature reviews from a pragmatic perspective. Our article aims to shed light on these issues and hopes to provide clarity for future scholarly endeavors.

Having a foundational understanding of literature reviews as independent studies is (i) necessary when addressing the aforementioned issues; (ii) important in reconciling and scaffolding our understanding, and (iii) relevant and timely due to the proliferation of literature reviews as independent studies. To contribute a solution toward addressing this gap , we aim to demystify review articles as independent studies from a pragmatic standpoint (i.e., practicality). To do so, we deliberately (i) move away from review procedures, protocols, and nomenclatures, and (ii) invest our attention in developing a parsimonious, scaffolded understanding of the fundamental elements (i.e., types, focuses, considerations, methods, and contributions) of review articles as independent studies.

Three contributions distinguish our article. It is worth noting that pragmatic guides (i.e., foundational knowledge), such as the present one, are not at odds with extant philosophical guides (i.e., advanced knowledge), but rather they complement them. Having a foundational knowledge of the fundamental elements of literature reviews as independent studies is valuable , as it can help scholars to (i) gain a good grasp of the fundamental elements of literature reviews as independent studies ( 1st contribution ), and (ii) mindfully adopt or adapt existing review procedures, protocols, and nomenclatures to better suit the circumstances of their reviews (e.g., choosing and developing a well-defined review nomenclature, and choosing and reporting on review considerations and steps more parsimoniously) ( 2nd contribution ). Therefore, this pragmatic guide serves as (iii) a foundational article (i.e., preparatory understanding) for literature reviews as independent studies ( 3rd contribution ). Following this, extant guides using a philosophical approach (i.e., advanced understanding) could be relied upon to make informed review decisions (e.g., adoption, adaptation) in response to the conventions of extant review procedures, protocols, and nomenclatures (Fig.  2 ).

Foundational and advanced understanding of literature reviews as independent studies

2 Fundamental elements of literature reviews as independent studies

A foundational understanding of literature reviews as independent studies can be acquired through the appreciation of five fundamental elements – i.e., types, focuses, considerations, methods, and contributions – which are illustrated in Fig.  3 and summarized in the following sections.

Fundamental elements of literature reviews as independent studies

There are two types of literature reviews as independent studies: systematic literature reviews ( SLRs ) and non-systematic literature reviews ( non-SLRs ). It is important to recognize that SLRs and non-SLRs are not review nomenclatures (i.e., names/naming) but rather review types (i.e., classifications).

In particular, SLRs are reviews carried out in a systematic way using an adopted or adapted procedure or protocol to guide data curation and analysis, thus enabling transparent disclosure and replicability (Lim et al. 2022a ; Kraus et al. 2020 ). Therefore, any review nomenclature guided by a systematic methodology is essentially an SLR. The origin of this type of literature review can be traced back to the evidence-based medicine movement in the early 1990s, with the objective being to overcome the issue of inconclusive findings in studies for medical treatments (Boell and Cecez-Kecmanovic 2015 ).

In contrast, non-SLRs are reviews conducted without any systematic procedure or protocol; instead, they weave together relevant literature based on the critical evaluations and (subjective) choices of the author(s) through a process of discovery and critique (e.g., pointing out contradictions and questioning assertions or beliefs); they are shaped by the exposure, expertise, and experience (i.e., the “3Es” in judgement calls) of the author(s). Therefore, non-SLRs are essentially critical reviews of the literature (Lim and Weissmann 2021 ).

2.2 Focuses

Unlike Palmatier et al. ( 2018 ) who considered domain-based reviews, theory-based reviews, and method-based reviews as review nomenclatures, we consider domain , theory , and method as three substantive focuses that can take center stage in literature reviews as independent studies. This is in line with our attempt to move away from review nomenclatures when providing a foundational understanding of literature reviews as independent studies.

A review that is domain-focused can examine: (i) a  concept (e.g., customer engagement; Lim et al. 2022b ; digital transformation; Kraus et al. 2021 ; home sharing; Lim et al. 2021 ; sharing economy; Lim 2020 ), (ii) a context (e.g., India; Mukherjee et al. 2022a ), (iii) a discipline (e.g., entrepreneurship; Ferreira et al. 2015 ; international business; Ghauri et al. 2021 ), (iv) a field (e.g., family business; Lahiri et al. 2020 ; Rovelli et al. 2021 ; female entrepreneurship; Ojong et al. 2021 ), or (v) an outlet (e.g., Journal of Business Research ; Donthu et al. 2020 ; Management International Review ; Mukherjee et al. 2021 ; Review of Managerial Science ; Mas-Tur et al. 2020 ), which typically offer broad, overarching insights.

Domain-focused hybrids , such as the between-domain hybrid (e.g., concept-discipline hybrid, such as digital transformation in business and management; Kraus et al. 2022 ; religion in business and entrepreneurship; Kumar et al. 2022a ; personality traits in entrepreneurship; Salmony and Kanbach 2022 ; and policy implications in HR and OB research; Aguinis et al., 2022 ) and the within-domain hybrid (e.g., the concept-concept hybrid, such as customer engagement and social media; Lim and Rasul 2022 ; and global business and organizational excellence; Lim 2022 ; and the discipline-discipline hybrid, such as neuromarketing; Lim 2018 ) are also common as they can provide finer-grained insights.

A review that is theory-focused can explore a standalone theory (e.g., theory of planned behavior; Duan and Jiang 2008 ), as well as a theory in conjunction with a domain , such as the concept-theory hybrid (e.g., behavioral control and theory of planned behavior; Lim and Weissmann 2021 ) and the theory-discipline hybrid (e.g., theory of planned behavior in hospitality, leisure, and tourism; Ulker-Demirel and Ciftci 2020 ), or a theory in conjunction with a method (e.g., theory of planned behavior and structural equation modeling).

A review that is method-focused can investigate a standalone method (e.g., structural equation modeling; Deng et al. 2018 ) or a method in conjunction with a domain , such as the method-discipline hybrid (e.g., fsQCA in business and management; Kumar et al. 2022b ).

2.3 Planning the review, critical considerations, and data collection

The considerations required for literature reviews as independent studies depend on their type: SLRs or non-SLRs.

For non-SLRs, scholars often rely on the 3Es (i.e., exposure, expertise, and experience) to provide a critical review of the literature. Scholars who embark on non-SLRs should be well versed with the literature they are dealing with. They should know the state of the literature (e.g., debatable, underexplored, and well-established knowledge areas) and how it needs to be deciphered (e.g., tenets and issues) and approached (e.g., reconciliation proposals and new pathways) to advance theory and practice. In this regard, non-SLRs follow a deductive reasoning approach, whereby scholars initially develop a set of coverage areas for reviewing a domain, theory, or method and subsequently draw on relevant literature to shed light and support scholarly contentions in each area.

For SLRs, scholars often rely on a set of criteria to provide a well-scoped (i.e., breadth and depth), structured (i.e., organized aspects), integrated (i.e., synthesized evidence) and interpreted/narrated (i.e., describing what has happened, how and why) systematic review of the literature. Footnote 2 In this regard, SLRs follow an inductive reasoning approach, whereby a set of criteria is established and implemented to develop a corpus of scholarly documents that scholars can review. They can then deliver a state-of-the-art overview, as well as a future agenda for a domain, theory, or method. Such criteria are often listed in philosophical guides on SLR procedures (e.g., Kraus et al. 2020 ; Snyder 2019 ) and protocols (e.g., PRISMA), and they may be adopted/adapted with justifications Footnote 3 . Based on their commonalities they can be summarized as follows:

Search database (e.g., “Scopus” and/or “Web of Science”) can be defined based on justified evidence (e.g., by the two being the largest scientific databases of scholarly articles that can provide on-demand bibliographic data or records; Pranckutė 2021 ). To avoid biased outcomes due to the scope covered by the selected database, researchers could utilize two or more different databases (Dabić et al. 2021 ).

Search keywords may be developed by reading scholarly documents and subsequently brainstorming with experts. The expanding number of databases, journals, periodicals, automated approaches, and semi-automated procedures that use text mining and machine learning can offer researchers the ability to source new, relevant research and forecast the citations of influential studies. This enables them to determine further relevant articles.

Boolean operators (e.g., AND, OR) should be strategically used in developing the  string   of search keywords (e.g., “engagement” AND “customer” OR “consumer” OR “business”). Furthermore, the correct and precise application of quotation marks is important but is very frequently sidestepped, resulting in incorrect selection processes and differentiated results.

Search period (e.g., between a specified period [e.g., 2000 to 2020] or up to the latest full year at the time or writing [e.g., up to 2021]) can be defined based on the justified scope of study (e.g., contemporary evolution versus historical trajectory).

Search field (e.g., “article title, abstract, keywords”) can be defined based on justified assumptions (e.g., it is assumed that the focus of relevant documents will be mentioned in the article title, abstract, and/or keywords).

Subject area (e.g., “business, management, and accounting”) can be defined based on justified principles (e.g., the focus of the review is on the marketing discipline, which is located under the “business, management, and accounting” subject area in Scopus).

Publication stage (e.g., “final”) can be defined based on justified grounds (e.g., enabling greater accuracy in replication).

Document type (e.g., “article” and/or “review”), which reflects the type of scientific/practical contributions (e.g., empirical, synthesis, thought), can be defined based on justified rationales (e.g., articles selected because they are peer-reviewed; editorials not selected because they are not peer-reviewed).

Source type (e.g., “journal”) can be defined based on justified reasons (e.g., journals selected because they publish finalized work; conference proceedings not selected because they are work in progress, and in business/management, they are usually not being considered as full-fledged “publications”).

Language (e.g., “English”) can be determined based on justified limitations (e.g., nowadays, there are not many reasons to use another language besides the academic lingua franca English). Different spellings should also be considered, as the literature may contain both American and British spelling variants (e.g., organization and organisation). Truncation and wildcards in searches are recommended to capture both sets of spellings. It is important to note that each database varies in its symbology.

Quality filtering (e.g., “A*” and “A” or “4*”, “4”, and “3”) can be defined based on justified motivations (e.g., the goal is to unpack the most originally and rigorously produced knowledge, which is the hallmark of premier journals, such as those ranked “A*” and “A” by the Australian Business Deans Council [ABDC] Journal Quality List [JQL] and rated “4*”, “4”, and “3” by the Chartered Association of Business Schools [CABS] Academic Journal Guide [AJG]).

Document relevance (i.e., within the focus of the review) can be defined based on justified judgement (e.g., for a review focusing on customer engagement, articles that mention customer engagement as a passing remark without actually investigating it would be excluded).

Others: Screening process should be accomplished by beginning with the deduction of duplicate results from other databases, tracked using abstract screening to exclude unfitting studies, and ending with the full-text screening of the remaining documents.

Others: Exclusion-inclusion criteria interpretation of the abstracts/articles is obligatory when deciding whether or not the articles dealt with the matter. This step could involve removing a huge percentage of initially recognized articles.

Others: Codebook building pertains to the development of a codebook of the main descriptors within a specific field. An inductive approach can be followed and, in this case, descriptors are not established beforehand. Instead, they are established through the analysis of the articles’ content. This procedure is made up of several stages: (i) the extraction of important content from titles, abstracts, and keywords; (ii) the classification of this content to form a reduced list of the core descriptors; and (iii) revising the codebook in iterations and combining similar categories, thus developing a short list of descriptors (López-Duarte et al. 2016 , p. 512; Dabić et al. 2015 ; Vlacic et al. 2021 ).

2.4 Methods

Various methods are used to analyze the pertinent literature. Often, scholars choose a method for corpus analysis before corpus curation. Knowing the analytical technique beforehand is useful, as it allows researchers to acquire and prepare the right data in the right format. This typically occurs when scholars have decided upon and justified pursuing a specific review nomenclature upfront (e.g., bibliometric reviews) based on the problem at hand (e.g., broad domain [outlet] with a large corpus [thousands of articles], such as a premier journal that has been publishing for decades) (Donthu et al. 2021 ). However, this may not be applicable in instances where (i) scholars do not curate a corpus of articles (non-SLRs), and (ii) scholars only know the size of the corpus of articles once that corpus is curated (SLRs). Therefore, scholars may wish to decide on a method of analyzing the literature depending on (i) whether they rely on a corpus of articles (i.e., yes or no), and (ii) the size of the corpus of articles that they rely on to review the literature (i.e., n  = 0 to ∞).

When analytical techniques (e.g., bibliometric analysis, critical analysis, meta-analysis) are decoupled from review nomenclatures (e.g., bibliometric reviews, critical reviews, meta-analytical reviews), we uncover a toolbox of the following methods for use when analyzing the literature:

Bibliometric analysis measures the literature and processes data by using algorithm, arithmetic, and statistics to analyze, explore, organize, and investigate large amounts of data. This enables scholars to identify and recognize potential “hidden patterns” that could help them during the literature review process. Bibliometrics allows scholars to objectively analyze a large corpus of articles (e.g., high hundreds or more) using quantitative techniques (Donthu et al. 2021 ). There are two overarching categories for bibliometric analysis: performance analysis and science mapping. Performance analysis enables scholars to assess the productivity (publication) and impact (citation) of the literature relating to a domain, method, or theory using various quantitative metrics (e.g., average citations per publication or year, h -index, g -index, i -index). Science mapping grants scholars the ability to map the literature in that domain, method, or theory based on bibliographic data (e.g., bibliographic coupling generates thematic clusters based on similarities in shared bibliographic data [e.g., references] among citing articles; co-citation analysis generates thematic clusters based on commonly cited articles; co-occurrence analysis generates thematic clusters based on bibliographic data [e.g., keywords] that commonly appear together; PageRank analysis generates thematic clusters based on articles that are commonly cited in highly cited articles; and topic modeling generates thematic clusters based on the natural language processing of bibliographic data [e.g., article title, abstract, and keywords]). Footnote 4 Given the advancement in algorithms and technology, reviews using bibliometric analysis are considered to be smart (Kraus et al. 2021 ) and technologically-empowered (Kumar et al. 2022b ) SLRs, in which a review has harnessed the benefits of (i) the machine learning of the bibliographic data of scholarly research from technologically-empowered scientific databases, and (ii) big data analytics involving various science mapping techniques (Kumar et al. 2022c ).

Content analysis allows scholars to analyze a small to medium corpus of articles (i.e., tens to low hundreds) using quantitative and qualitative techniques. From a quantitative perspective , scholars can objectively carry out a content analysis by quantifying a specific unit of analysis . A useful method of doing so involves adopting, adapting, or developing an organizing framework . For example, Lim et al. ( 2021 ) employed an organizing (ADO-TCM) framework to quantify content in academic literature based on: (i) the categories of knowledge; (ii) the relationships between antecedents, decisions, and outcomes; and (iii) the theories, contexts, and methods used to develop the understanding for (i) and (ii). The rapid evolution of software for content analysis allows scholars to carry out complex elaborations on the corpus of analyzed articles, so much so that the most recent software enables the semi-automatic development of an organizing framework (Ammirato et al. 2022 ). From a qualitative perspective , scholars can conduct a content analysis or, more specifically, a thematic analysis , by subjectively organizing the content into themes. For example, Creevey et al. ( 2022 ) reviewed the literature on social media and luxury, providing insights on five core themes (i.e., luxury brand strategy, luxury brand social media communications, luxury consumer attitudes and perceptions, engagement, and the influence of social media on brand performance-related outcomes) generated through a content (thematic) analysis. Systematic approaches for inductive concept development through qualitative research are similarly applied in literature reviews in an attempt to reduce the subjectivity of derived themes. Following the principles of the approach by Gioia et al. ( 2012 ), Korherr and Kanbach ( 2021 ) develop a taxonomy of human-related capabilities in big data analytics. Building on a sample of 75 studies for the literature review, 33 first-order concepts are identified. These are categorized into 15 second-order themes and are finally merged into five aggregate dimensions. Using the same procedure, Leemann and Kanbach ( 2022 ) identify 240 idiosyncratic dynamic capabilities in a sample of 34 studies for their literature review. They then categorize these into 19 dynamic sub-capabilities. The advancement of technology also makes it possible to conduct content analysis using computer assisted qualitative data analysis (CAQDA) software (e.g., ATLAS.ti, Nvivo, Quirkos) (Lim et al. 2022a ).

Critical analysis allows scholars to subjectively use their 3Es (i.e., exposure, expertise, and experience) to provide a critical evaluation of academic literature. This analysis is typically used in non-SLRs, and can be deployed in tandem with other analyses, such as bibliometric analysis and content analysis in SLRs, which are used to discuss consensual, contradictory, and underexplored areas of the literature. For SLRs, scholars are encouraged to engage in critical evaluations of the literature so that they can truly contribute to advancing theory and practice (Baker et al. 2022 ; Lim et al. 2022a ; Mukherjee et al. 2022b ).

Meta-analysis allows scholars to objectively establish a quantitative estimate of commonly studied relationships in the literature (Grewal et al. 2018 ). This analysis is typically employed in SLRs intending to reconcile a myriad of relationships (Lim et al. 2022a ). The relationships established are often made up of conflicting evidence (e.g., a positive or significant effect in one study, but a negative or non-significant effect in another study). However, through meta-analysis, scholars are able to identify potential factors (e.g., contexts or sociodemographic information) that may have led to the conflict.

Others: Multiple correspondence analysis helps to map the field, assessing the associations between qualitative content within a matrix of variables and cases. Homogeneity Analysis by Means of Alternating Least Squares ( HOMALS ) is also considered useful in allowing researchers to map out the intellectual structure of a variety of research fields (Gonzalez-Loureiro et al. 2015 ; Gonzalez-Louriero 2021; Obradović et al. 2021 ). HOMALS can be performed in R or used along with a matrix through SPSS software. In summary, the overall objective of this analysis is to discover a low dimensional representation of the original high dimensional space (i.e., the matrix of descriptors and articles). To measure the goodness of fit, a loss function is used. This function is used minimally, and the HOMALS algorithm is applied to the least squares loss functions in SPSS. This analysis provides a proximity map, in which articles and descriptors are shown in low-dimensional spaces (typically on two axes). Keywords are paired and each couple that appears together in a large number of articles is shown to be closer on the map and vice-versa.

When conducting a literature review, software solutions allow researchers to cover a broad range of variables, from built-in functions of statistical software packages to software orientated towards meta-analyses, and from commercial to open-source solutions. Personal preference plays a huge role, but the decision as to which software will be the most useful is entirely dependent on how complex the methods and the dataset are. Of all the commercial software providers, we have found the built-in functions of (i) R and VOSviewer most useful in performing bibliometric analysis (Aria and Cuccurullo 2017 ; R Core Team 2021 ; Van Eck and Waltman 2014 ) and (ii) Stata most useful in performing meta-analytical tasks.

Many different analytical tools have been used. These include simple document counting, citation analysis, word frequency analysis, cluster analysis, co-word analysis, and cooperation analysis (Daim et al. 2006 ). Software has also been produced for bibliometric analysis, such as the Thomson Data Analyzer (TDA), which Thomson Reuters created, and CiteSpace developed by Chen ( 2013 ). VOSviewer helps us to construct and visualize bibliometric networks, which can include articles, journals, authors, countries, and institutions, among others (Van Eck and Waltman 2014 ). These can be organized based on citations, co-citations, bibliographic coupling, or co-authorship relations. In addition, VOSviewer provides text mining functions, which can be used to facilitate a better understanding of co-occurrence networks with regards to the key terms taken from a body of scientific literature (Donthu et al. 2021 ; Wong 2018 ). Other frequently used tools include for bibliometric analysis include Bibliometrix/Biblioshiny in R, CitNetExplorer, and Gephi, among others.

2.5 Contributions

Well-conducted literature reviews may make multiple contributions to the literature as standalone, independent studies.

Generally, there are three primary contributions of literature reviews as independent studies: (i) to provide an overview of current knowledge in the domain, method, or theory, (ii) to provide an evaluation of knowledge progression in the domain, method, or theory, including the establishment of key knowledge, conflicting or inconclusive findings, and emerging and underexplored areas, and (iii) to provide a proposal for potential pathways for advancing knowledge in the domain, method, or theory (Lim et al. 2022a , p. 487). Developing theory through literature reviews can take many forms, including organizing and categorizing the literature, problematizing the literature, identifying and exposing contradictions, developing analogies and metaphors, and setting out new narratives and conceptualizations (Breslin and Gatrell 2020 ). Taken collectively, these contributions offer crystalized, evidence-based insights that both ‘mine’ and ‘prospect’ the literature, highlighting extant gaps and how they can be resolved (e.g., flags paradoxes or theoretical tensions, explaining why something has not been done, what the challenges are, and how these challenges can be overcome). These contributions can be derived through successful bibliometric analysis, content analysis, critical analysis, and meta-analysis.

Additionally, the deployment of specific methods can bring in further added value. For example, a performance analysis in a bibliometric analysis can contribute to: (i) objectively assessing and reporting research productivity and impact ; (ii) ascertaining reach for coverage claims ; (iii) identifying social dominance and hidden biases ; (iv) detecting anomalies ; and (v) evaluating ( equitable ) relative performance ; whereas science mapping in bibliometric analysis can contribute to: (i) objectively discovering thematic clusters of knowledge ; (ii) clarifying nomological networks ; (iii) mapping social patterns ; (iv) tracking evolutionary nuances ; and (v) recognizing knowledge gaps (Mukherjee et al. 2022b , p. 105).

3 Conclusion

Independent literature reviews will continue to be written as a result of their necessity, importance, relevance, and urgency when it comes to advancing knowledge (Lim et al. 2022a ; Mukherjee et al. 2022b ), and this can be seen in the increasing number of reviews being published over the last several years. Literature reviews advance academic discussion. Journal publications on various topics and subject areas are becoming more frequent sites for publication. This trend will only heighten the need for literature reviews. This article offers directions and control points that address the needs of three different stakeholder groups: producers (i.e., potential authors), evaluators (i.e., journal editors and reviewers), and users (i.e., new researchers looking to learn more about a particular methodological issue, and those teaching the next generation of scholars). Future producers will derive value from this article’s teachings on the different fundamental elements and methodological nuances of literature reviews. Procedural knowledge (i.e., using control points to assist in decision-making during the manuscript preparation phase) will also be of use. Evaluators will be able to make use of the procedural and declarative knowledge evident in control points as well. As previously outlined, the need to cultivate novelty within research on business and management practices is vital. Scholars must also be supported to choose not only safe mining approaches; they should also be encouraged to attempt more challenging and risky ventures. It is important to note that abstracts often seem to offer a lot of potential, stating that authors intend to make large conceptual contributions, broadening the horizons of the field.

Our article offers important insights also for practitioners. Noteworthily, our framework can support corporate managers in decomposing and better understanding literature reviews as ad-hoc and independent studies about specific topics that matter for their organization. For instance, practitioners can understand more easily what are the emerging trends within their domain of interest and make corporate decisions in line with such trends.

This article arises from an intentional decoupling from philosophy, in favor of adopting a more pragmatic approach. This approach can assist us in clarifying the fundamental elements of literature reviews as independent studies. Five fundamental elements must be considered: types, focuses, considerations, methods, and contributions. These elements offer a useful frame for scholars starting to work on a literature review. Overview articles (guides) such as ours are thus invaluable, as they equip scholars with a solid foundational understanding of the integral elements of a literature review. Scholars can then put these teachings into practice, armed with a better understanding of the philosophy that underpins the procedures, protocols, and nomenclatures of literature reviews as independent studies.

Data availability

Our manuscript has no associate data.

Our focus here is on standalone literature reviews in contrast with literature reviews that form the theoretical foundation for a research article.

Scoping reviews, structured reviews, integrative reviews, and interpretive/narrative reviews are commonly found in review nomenclature. However, the philosophy of these review nomenclatures essentially reflects what constitutes a good SLR. That is to say, a good SLR should be well scoped, structured, integrated, and interpreted/narrated. This observation reaffirms our position and the value of moving away from review nomenclatures to gain a foundational understanding of literature reviews as independent studies.

Given that many of these considerations can be implemented simultaneously in contemporary versions of scientific databases, scholars may choose to consolidate them into a single (or a few) step(s), where appropriate, so that they can be reported more parsimoniously. For a parsimonious but transparent and replicable exemplar, see Lim ( 2022 ).

Where keywords are present (e.g., author keywords or keywords derived from machine learning [e.g., natural language processing]), it is assumed that each keyword represents a specific meaning (e.g., topic [concept, context], method), and that a collection of keywords grouped under the same cluster represents a specific theme.

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Kraus, S., Breier, M., Lim, W.M. et al. Literature reviews as independent studies: guidelines for academic practice. Rev Manag Sci 16 , 2577–2595 (2022). https://doi.org/10.1007/s11846-022-00588-8

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Ten Simple Rules for Writing a Literature Review

* E-mail: [email protected]

Affiliations Centre for Functional and Evolutionary Ecology (CEFE), CNRS, Montpellier, France, Centre for Biodiversity Synthesis and Analysis (CESAB), FRB, Aix-en-Provence, France

• Marco Pautasso

Published: July 18, 2013

• https://doi.org/10.1371/journal.pcbi.1003149
• Reader Comments

Citation: Pautasso M (2013) Ten Simple Rules for Writing a Literature Review. PLoS Comput Biol 9(7): e1003149. https://doi.org/10.1371/journal.pcbi.1003149

Editor: Philip E. Bourne, University of California San Diego, United States of America

Copyright: © 2013 Marco Pautasso. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: This work was funded by the French Foundation for Research on Biodiversity (FRB) through its Centre for Synthesis and Analysis of Biodiversity data (CESAB), as part of the NETSEED research project. The funders had no role in the preparation of the manuscript.

Competing interests: The author has declared that no competing interests exist.

Literature reviews are in great demand in most scientific fields. Their need stems from the ever-increasing output of scientific publications [1] . For example, compared to 1991, in 2008 three, eight, and forty times more papers were indexed in Web of Science on malaria, obesity, and biodiversity, respectively [2] . Given such mountains of papers, scientists cannot be expected to examine in detail every single new paper relevant to their interests [3] . Thus, it is both advantageous and necessary to rely on regular summaries of the recent literature. Although recognition for scientists mainly comes from primary research, timely literature reviews can lead to new synthetic insights and are often widely read [4] . For such summaries to be useful, however, they need to be compiled in a professional way [5] .

When starting from scratch, reviewing the literature can require a titanic amount of work. That is why researchers who have spent their career working on a certain research issue are in a perfect position to review that literature. Some graduate schools are now offering courses in reviewing the literature, given that most research students start their project by producing an overview of what has already been done on their research issue [6] . However, it is likely that most scientists have not thought in detail about how to approach and carry out a literature review.

Reviewing the literature requires the ability to juggle multiple tasks, from finding and evaluating relevant material to synthesising information from various sources, from critical thinking to paraphrasing, evaluating, and citation skills [7] . In this contribution, I share ten simple rules I learned working on about 25 literature reviews as a PhD and postdoctoral student. Ideas and insights also come from discussions with coauthors and colleagues, as well as feedback from reviewers and editors.

Rule 1: Define a Topic and Audience

How to choose which topic to review? There are so many issues in contemporary science that you could spend a lifetime of attending conferences and reading the literature just pondering what to review. On the one hand, if you take several years to choose, several other people may have had the same idea in the meantime. On the other hand, only a well-considered topic is likely to lead to a brilliant literature review [8] . The topic must at least be:

• interesting to you (ideally, you should have come across a series of recent papers related to your line of work that call for a critical summary),
• an important aspect of the field (so that many readers will be interested in the review and there will be enough material to write it), and
• a well-defined issue (otherwise you could potentially include thousands of publications, which would make the review unhelpful).

Ideas for potential reviews may come from papers providing lists of key research questions to be answered [9] , but also from serendipitous moments during desultory reading and discussions. In addition to choosing your topic, you should also select a target audience. In many cases, the topic (e.g., web services in computational biology) will automatically define an audience (e.g., computational biologists), but that same topic may also be of interest to neighbouring fields (e.g., computer science, biology, etc.).

Rule 2: Search and Re-search the Literature

After having chosen your topic and audience, start by checking the literature and downloading relevant papers. Five pieces of advice here:

• keep track of the search items you use (so that your search can be replicated [10] ),
• keep a list of papers whose pdfs you cannot access immediately (so as to retrieve them later with alternative strategies),
• use a paper management system (e.g., Mendeley, Papers, Qiqqa, Sente),
• define early in the process some criteria for exclusion of irrelevant papers (these criteria can then be described in the review to help define its scope), and
• do not just look for research papers in the area you wish to review, but also seek previous reviews.

The chances are high that someone will already have published a literature review ( Figure 1 ), if not exactly on the issue you are planning to tackle, at least on a related topic. If there are already a few or several reviews of the literature on your issue, my advice is not to give up, but to carry on with your own literature review,

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The bottom-right situation (many literature reviews but few research papers) is not just a theoretical situation; it applies, for example, to the study of the impacts of climate change on plant diseases, where there appear to be more literature reviews than research studies [33] .

https://doi.org/10.1371/journal.pcbi.1003149.g001

• discussing in your review the approaches, limitations, and conclusions of past reviews,
• trying to find a new angle that has not been covered adequately in the previous reviews, and
• incorporating new material that has inevitably accumulated since their appearance.

When searching the literature for pertinent papers and reviews, the usual rules apply:

• be thorough,
• use different keywords and database sources (e.g., DBLP, Google Scholar, ISI Proceedings, JSTOR Search, Medline, Scopus, Web of Science), and
• look at who has cited past relevant papers and book chapters.

Rule 3: Take Notes While Reading

If you read the papers first, and only afterwards start writing the review, you will need a very good memory to remember who wrote what, and what your impressions and associations were while reading each single paper. My advice is, while reading, to start writing down interesting pieces of information, insights about how to organize the review, and thoughts on what to write. This way, by the time you have read the literature you selected, you will already have a rough draft of the review.

Of course, this draft will still need much rewriting, restructuring, and rethinking to obtain a text with a coherent argument [11] , but you will have avoided the danger posed by staring at a blank document. Be careful when taking notes to use quotation marks if you are provisionally copying verbatim from the literature. It is advisable then to reformulate such quotes with your own words in the final draft. It is important to be careful in noting the references already at this stage, so as to avoid misattributions. Using referencing software from the very beginning of your endeavour will save you time.

Rule 4: Choose the Type of Review You Wish to Write

After having taken notes while reading the literature, you will have a rough idea of the amount of material available for the review. This is probably a good time to decide whether to go for a mini- or a full review. Some journals are now favouring the publication of rather short reviews focusing on the last few years, with a limit on the number of words and citations. A mini-review is not necessarily a minor review: it may well attract more attention from busy readers, although it will inevitably simplify some issues and leave out some relevant material due to space limitations. A full review will have the advantage of more freedom to cover in detail the complexities of a particular scientific development, but may then be left in the pile of the very important papers “to be read” by readers with little time to spare for major monographs.

There is probably a continuum between mini- and full reviews. The same point applies to the dichotomy of descriptive vs. integrative reviews. While descriptive reviews focus on the methodology, findings, and interpretation of each reviewed study, integrative reviews attempt to find common ideas and concepts from the reviewed material [12] . A similar distinction exists between narrative and systematic reviews: while narrative reviews are qualitative, systematic reviews attempt to test a hypothesis based on the published evidence, which is gathered using a predefined protocol to reduce bias [13] , [14] . When systematic reviews analyse quantitative results in a quantitative way, they become meta-analyses. The choice between different review types will have to be made on a case-by-case basis, depending not just on the nature of the material found and the preferences of the target journal(s), but also on the time available to write the review and the number of coauthors [15] .

Rule 5: Keep the Review Focused, but Make It of Broad Interest

Whether your plan is to write a mini- or a full review, it is good advice to keep it focused 16 , 17 . Including material just for the sake of it can easily lead to reviews that are trying to do too many things at once. The need to keep a review focused can be problematic for interdisciplinary reviews, where the aim is to bridge the gap between fields [18] . If you are writing a review on, for example, how epidemiological approaches are used in modelling the spread of ideas, you may be inclined to include material from both parent fields, epidemiology and the study of cultural diffusion. This may be necessary to some extent, but in this case a focused review would only deal in detail with those studies at the interface between epidemiology and the spread of ideas.

While focus is an important feature of a successful review, this requirement has to be balanced with the need to make the review relevant to a broad audience. This square may be circled by discussing the wider implications of the reviewed topic for other disciplines.

Rule 6: Be Critical and Consistent

Reviewing the literature is not stamp collecting. A good review does not just summarize the literature, but discusses it critically, identifies methodological problems, and points out research gaps [19] . After having read a review of the literature, a reader should have a rough idea of:

• the major achievements in the reviewed field,
• the main areas of debate, and
• the outstanding research questions.

It is challenging to achieve a successful review on all these fronts. A solution can be to involve a set of complementary coauthors: some people are excellent at mapping what has been achieved, some others are very good at identifying dark clouds on the horizon, and some have instead a knack at predicting where solutions are going to come from. If your journal club has exactly this sort of team, then you should definitely write a review of the literature! In addition to critical thinking, a literature review needs consistency, for example in the choice of passive vs. active voice and present vs. past tense.

Rule 7: Find a Logical Structure

Like a well-baked cake, a good review has a number of telling features: it is worth the reader's time, timely, systematic, well written, focused, and critical. It also needs a good structure. With reviews, the usual subdivision of research papers into introduction, methods, results, and discussion does not work or is rarely used. However, a general introduction of the context and, toward the end, a recapitulation of the main points covered and take-home messages make sense also in the case of reviews. For systematic reviews, there is a trend towards including information about how the literature was searched (database, keywords, time limits) [20] .

How can you organize the flow of the main body of the review so that the reader will be drawn into and guided through it? It is generally helpful to draw a conceptual scheme of the review, e.g., with mind-mapping techniques. Such diagrams can help recognize a logical way to order and link the various sections of a review [21] . This is the case not just at the writing stage, but also for readers if the diagram is included in the review as a figure. A careful selection of diagrams and figures relevant to the reviewed topic can be very helpful to structure the text too [22] .

Rule 8: Make Use of Feedback

Reviews of the literature are normally peer-reviewed in the same way as research papers, and rightly so [23] . As a rule, incorporating feedback from reviewers greatly helps improve a review draft. Having read the review with a fresh mind, reviewers may spot inaccuracies, inconsistencies, and ambiguities that had not been noticed by the writers due to rereading the typescript too many times. It is however advisable to reread the draft one more time before submission, as a last-minute correction of typos, leaps, and muddled sentences may enable the reviewers to focus on providing advice on the content rather than the form.

Feedback is vital to writing a good review, and should be sought from a variety of colleagues, so as to obtain a diversity of views on the draft. This may lead in some cases to conflicting views on the merits of the paper, and on how to improve it, but such a situation is better than the absence of feedback. A diversity of feedback perspectives on a literature review can help identify where the consensus view stands in the landscape of the current scientific understanding of an issue [24] .

Rule 9: Include Your Own Relevant Research, but Be Objective

In many cases, reviewers of the literature will have published studies relevant to the review they are writing. This could create a conflict of interest: how can reviewers report objectively on their own work [25] ? Some scientists may be overly enthusiastic about what they have published, and thus risk giving too much importance to their own findings in the review. However, bias could also occur in the other direction: some scientists may be unduly dismissive of their own achievements, so that they will tend to downplay their contribution (if any) to a field when reviewing it.

In general, a review of the literature should neither be a public relations brochure nor an exercise in competitive self-denial. If a reviewer is up to the job of producing a well-organized and methodical review, which flows well and provides a service to the readership, then it should be possible to be objective in reviewing one's own relevant findings. In reviews written by multiple authors, this may be achieved by assigning the review of the results of a coauthor to different coauthors.

Rule 10: Be Up-to-Date, but Do Not Forget Older Studies

Given the progressive acceleration in the publication of scientific papers, today's reviews of the literature need awareness not just of the overall direction and achievements of a field of inquiry, but also of the latest studies, so as not to become out-of-date before they have been published. Ideally, a literature review should not identify as a major research gap an issue that has just been addressed in a series of papers in press (the same applies, of course, to older, overlooked studies (“sleeping beauties” [26] )). This implies that literature reviewers would do well to keep an eye on electronic lists of papers in press, given that it can take months before these appear in scientific databases. Some reviews declare that they have scanned the literature up to a certain point in time, but given that peer review can be a rather lengthy process, a full search for newly appeared literature at the revision stage may be worthwhile. Assessing the contribution of papers that have just appeared is particularly challenging, because there is little perspective with which to gauge their significance and impact on further research and society.

Inevitably, new papers on the reviewed topic (including independently written literature reviews) will appear from all quarters after the review has been published, so that there may soon be the need for an updated review. But this is the nature of science [27] – [32] . I wish everybody good luck with writing a review of the literature.

Acknowledgments

Many thanks to M. Barbosa, K. Dehnen-Schmutz, T. Döring, D. Fontaneto, M. Garbelotto, O. Holdenrieder, M. Jeger, D. Lonsdale, A. MacLeod, P. Mills, M. Moslonka-Lefebvre, G. Stancanelli, P. Weisberg, and X. Xu for insights and discussions, and to P. Bourne, T. Matoni, and D. Smith for helpful comments on a previous draft.

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What is a literature review?

A literature review is an integrated analysis -- not just a summary-- of scholarly writings and other relevant evidence related directly to your research question.  That is, it represents a synthesis of the evidence that provides background information on your topic and shows a association between the evidence and your research question.

A literature review may be a stand alone work or the introduction to a larger research paper, depending on the assignment.  Rely heavily on the guidelines your instructor has given you.

Why is it important?

A literature review is important because it:

• Explains the background of research on a topic.
• Demonstrates why a topic is significant to a subject area.
• Discovers relationships between research studies/ideas.
• Identifies major themes, concepts, and researchers on a topic.
• Identifies critical gaps and points of disagreement.
• Discusses further research questions that logically come out of the previous studies.

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1. Choose a topic. Define your research question.

Your literature review should be guided by your central research question.  The literature represents background and research developments related to a specific research question, interpreted and analyzed by you in a synthesized way.

• Make sure your research question is not too broad or too narrow.  Is it manageable?
• Begin writing down terms that are related to your question. These will be useful for searches later.
• If you have the opportunity, discuss your topic with your professor and your class mates.

2. Decide on the scope of your review

How many studies do you need to look at? How comprehensive should it be? How many years should it cover? 

• This may depend on your assignment.  How many sources does the assignment require?

3. Select the databases you will use to conduct your searches.

Make a list of the databases you will search. 

Where to find databases:

• use the tabs on this guide
• Find other databases in the Nursing Information Resources web page
• More on the Medical Library web page
• ... and more on the Yale University Library web page

4. Conduct your searches to find the evidence. Keep track of your searches.

• Use the key words in your question, as well as synonyms for those words, as terms in your search. Use the database tutorials for help.
• Save the searches in the databases. This saves time when you want to redo, or modify, the searches. It is also helpful to use as a guide is the searches are not finding any useful results.
• Review the abstracts of research studies carefully. This will save you time.
• Use the bibliographies and references of research studies you find to locate others.
• Check with your professor, or a subject expert in the field, if you are missing any key works in the field.
• Ask your librarian for help at any time.
• Use a citation manager, such as EndNote as the repository for your citations. See the EndNote tutorials for help.

Review the literature

Some questions to help you analyze the research:

• What was the research question of the study you are reviewing? What were the authors trying to discover?
• Was the research funded by a source that could influence the findings?
• What were the research methodologies? Analyze its literature review, the samples and variables used, the results, and the conclusions.
• Does the research seem to be complete? Could it have been conducted more soundly? What further questions does it raise?
• If there are conflicting studies, why do you think that is?
• How are the authors viewed in the field? Has this study been cited? If so, how has it been analyzed?

Tips: 

• Review the abstracts carefully.  
• Keep careful notes so that you may track your thought processes during the research process.
• Create a matrix of the studies for easy analysis, and synthesis, across all of the studies.
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• http://orcid.org/0000-0003-0157-5319 Ahtisham Younas 1 , 2 ,
• http://orcid.org/0000-0002-7839-8130 Parveen Ali 3 , 4
• 1 Memorial University of Newfoundland , St John's , Newfoundland , Canada
• 2 Swat College of Nursing , Pakistan
• 3 School of Nursing and Midwifery , University of Sheffield , Sheffield , South Yorkshire , UK
• 4 Sheffield University Interpersonal Violence Research Group , Sheffield University , Sheffield , UK
• Correspondence to Ahtisham Younas, Memorial University of Newfoundland, St John's, NL A1C 5C4, Canada; ay6133{at}mun.ca

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Introduction

Literature reviews offer a critical synthesis of empirical and theoretical literature to assess the strength of evidence, develop guidelines for practice and policymaking, and identify areas for future research. 1 It is often essential and usually the first task in any research endeavour, particularly in masters or doctoral level education. For effective data extraction and rigorous synthesis in reviews, the use of literature summary tables is of utmost importance. A literature summary table provides a synopsis of an included article. It succinctly presents its purpose, methods, findings and other relevant information pertinent to the review. The aim of developing these literature summary tables is to provide the reader with the information at one glance. Since there are multiple types of reviews (eg, systematic, integrative, scoping, critical and mixed methods) with distinct purposes and techniques, 2 there could be various approaches for developing literature summary tables making it a complex task specialty for the novice researchers or reviewers. Here, we offer five tips for authors of the review articles, relevant to all types of reviews, for creating useful and relevant literature summary tables. We also provide examples from our published reviews to illustrate how useful literature summary tables can be developed and what sort of information should be provided.

Tip 1: provide detailed information about frameworks and methods

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Tabular literature summaries from a scoping review. Source: Rasheed et al . 3

The provision of information about conceptual and theoretical frameworks and methods is useful for several reasons. First, in quantitative (reviews synthesising the results of quantitative studies) and mixed reviews (reviews synthesising the results of both qualitative and quantitative studies to address a mixed review question), it allows the readers to assess the congruence of the core findings and methods with the adapted framework and tested assumptions. In qualitative reviews (reviews synthesising results of qualitative studies), this information is beneficial for readers to recognise the underlying philosophical and paradigmatic stance of the authors of the included articles. For example, imagine the authors of an article, included in a review, used phenomenological inquiry for their research. In that case, the review authors and the readers of the review need to know what kind of (transcendental or hermeneutic) philosophical stance guided the inquiry. Review authors should, therefore, include the philosophical stance in their literature summary for the particular article. Second, information about frameworks and methods enables review authors and readers to judge the quality of the research, which allows for discerning the strengths and limitations of the article. For example, if authors of an included article intended to develop a new scale and test its psychometric properties. To achieve this aim, they used a convenience sample of 150 participants and performed exploratory (EFA) and confirmatory factor analysis (CFA) on the same sample. Such an approach would indicate a flawed methodology because EFA and CFA should not be conducted on the same sample. The review authors must include this information in their summary table. Omitting this information from a summary could lead to the inclusion of a flawed article in the review, thereby jeopardising the review’s rigour.

Tip 2: include strengths and limitations for each article

Critical appraisal of individual articles included in a review is crucial for increasing the rigour of the review. Despite using various templates for critical appraisal, authors often do not provide detailed information about each reviewed article’s strengths and limitations. Merely noting the quality score based on standardised critical appraisal templates is not adequate because the readers should be able to identify the reasons for assigning a weak or moderate rating. Many recent critical appraisal checklists (eg, Mixed Methods Appraisal Tool) discourage review authors from assigning a quality score and recommend noting the main strengths and limitations of included studies. It is also vital that methodological and conceptual limitations and strengths of the articles included in the review are provided because not all review articles include empirical research papers. Rather some review synthesises the theoretical aspects of articles. Providing information about conceptual limitations is also important for readers to judge the quality of foundations of the research. For example, if you included a mixed-methods study in the review, reporting the methodological and conceptual limitations about ‘integration’ is critical for evaluating the study’s strength. Suppose the authors only collected qualitative and quantitative data and did not state the intent and timing of integration. In that case, the strength of the study is weak. Integration only occurred at the levels of data collection. However, integration may not have occurred at the analysis, interpretation and reporting levels.

Tip 3: write conceptual contribution of each reviewed article

While reading and evaluating review papers, we have observed that many review authors only provide core results of the article included in a review and do not explain the conceptual contribution offered by the included article. We refer to conceptual contribution as a description of how the article’s key results contribute towards the development of potential codes, themes or subthemes, or emerging patterns that are reported as the review findings. For example, the authors of a review article noted that one of the research articles included in their review demonstrated the usefulness of case studies and reflective logs as strategies for fostering compassion in nursing students. The conceptual contribution of this research article could be that experiential learning is one way to teach compassion to nursing students, as supported by case studies and reflective logs. This conceptual contribution of the article should be mentioned in the literature summary table. Delineating each reviewed article’s conceptual contribution is particularly beneficial in qualitative reviews, mixed-methods reviews, and critical reviews that often focus on developing models and describing or explaining various phenomena. Figure 2 offers an example of a literature summary table. 4

Tabular literature summaries from a critical review. Source: Younas and Maddigan. 4

Tip 4: compose potential themes from each article during summary writing

While developing literature summary tables, many authors use themes or subthemes reported in the given articles as the key results of their own review. Such an approach prevents the review authors from understanding the article’s conceptual contribution, developing rigorous synthesis and drawing reasonable interpretations of results from an individual article. Ultimately, it affects the generation of novel review findings. For example, one of the articles about women’s healthcare-seeking behaviours in developing countries reported a theme ‘social-cultural determinants of health as precursors of delays’. Instead of using this theme as one of the review findings, the reviewers should read and interpret beyond the given description in an article, compare and contrast themes, findings from one article with findings and themes from another article to find similarities and differences and to understand and explain bigger picture for their readers. Therefore, while developing literature summary tables, think twice before using the predeveloped themes. Including your themes in the summary tables (see figure 1 ) demonstrates to the readers that a robust method of data extraction and synthesis has been followed.

Tip 5: create your personalised template for literature summaries

Often templates are available for data extraction and development of literature summary tables. The available templates may be in the form of a table, chart or a structured framework that extracts some essential information about every article. The commonly used information may include authors, purpose, methods, key results and quality scores. While extracting all relevant information is important, such templates should be tailored to meet the needs of the individuals’ review. For example, for a review about the effectiveness of healthcare interventions, a literature summary table must include information about the intervention, its type, content timing, duration, setting, effectiveness, negative consequences, and receivers and implementers’ experiences of its usage. Similarly, literature summary tables for articles included in a meta-synthesis must include information about the participants’ characteristics, research context and conceptual contribution of each reviewed article so as to help the reader make an informed decision about the usefulness or lack of usefulness of the individual article in the review and the whole review.

In conclusion, narrative or systematic reviews are almost always conducted as a part of any educational project (thesis or dissertation) or academic or clinical research. Literature reviews are the foundation of research on a given topic. Robust and high-quality reviews play an instrumental role in guiding research, practice and policymaking. However, the quality of reviews is also contingent on rigorous data extraction and synthesis, which require developing literature summaries. We have outlined five tips that could enhance the quality of the data extraction and synthesis process by developing useful literature summaries.

• Aromataris E ,
• Rasheed SP ,

Twitter @Ahtisham04, @parveenazamali

Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

Competing interests None declared.

Patient consent for publication Not required.

Provenance and peer review Not commissioned; externally peer reviewed.

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• Systematic Review
• Open access
• Published: 25 August 2024

Immediate and long-term efficacy of transcranial direct current stimulation (tCDS) in obsessive-compulsive disorder, posttraumatic stress disorder and anxiety disorders: a systematic review and meta-analysis

• Luxin Xie 1 , 2 ,
• Peina Hu 1 , 2 ,
• Zhenglong Guo 1 ,
• Miao Chen 1 ,
• Xiao Wang   ORCID: orcid.org/0000-0003-2842-4975 1 , 3 ,
• Xinzhe Du 1 , 3 ,
• Yue Li 1 , 3 ,
• Bo Chen 4 ,
• Jihui Zhang 4 ,
• Wentao Zhao   ORCID: orcid.org/0000-0001-8015-5851 1 , 3 &
• Sha Liu   ORCID: orcid.org/0000-0002-6710-8126 1 , 3  

Translational Psychiatry volume  14 , Article number:  343 ( 2024 ) Cite this article

Metrics details

• Psychiatric disorders

Currently, there is still debate over the effectiveness of transcranial direct current stimulation (tDCS) in treating obsessive-compulsive disorder (OCD), posttraumatic stress disorder (PTSD) and anxiety disorders (ADs). To investigate the immediate and long-term effectiveness of tDCS in these diseases, we conducted a systematic review and quantitative analysis of existing literature on the treatment of OCD, PTSD, and ADs with tDCS. Following the PRISMA guidelines, we searched seven electronic databases and systematically retrieved articles published from May 2012 to June 2024 that compared the effects of active tDCS with sham stimulation in the treatment of these disorders. We included primary outcome measures such as the change scores in disorder-specific and general anxiety symptoms before and after treatment, as well as secondary outcomes such as changes in disorder-specific and general anxiety symptoms at follow-up. We also assessed the impact of tDCS on depressive symptoms. Fifteen papers met the eligibility criteria. Overall, the results of meta-analysis indicated that tDCS had a high effect in improving specific symptoms (SMD = −0.73, 95% CI: −1.09 to −0.37) and general anxiety symptoms (SMD = −0.75; 95% CI: −1.23 to −0.26) in OCD, PTSD and ADs, with effects lasting up to 1 month and showing a moderate effect size. Furthermore, tDCS demonstrated immediate and significant alleviation of depressive symptoms in these diseases. This study concludes that tDCS can serve as a non-invasive brain stimulation technology for treating these disorders, and the therapeutic effects can be maintained for a period of time.

Introduction

The lifetime prevalence of obsessive-compulsive disorder (OCD), posttraumatic stress disorder (PTSD) and anxiety disorders (ADs) is approximately 21%, with an annual incidence of 14% [ 1 ]. These disorders share some basic clinical features, including excessive and persistent anxiety, attention bias towards threatening stimuli, hyperarousal and avoidance [ 2 ]. Therefore, the similar approaches would be applied composing drug treatment with selective serotonin reuptake inhibitors (SSRIs) and psychological intervention with cognitive behavioral therapy (CBT) [ 3 , 4 , 5 ]. However, the side effects of drug and issues such as the cost and commitment limitations of psychotherapy hinder adherence and affect treatment. About 30% of patients still cannot receive effective treatment [ 6 , 7 , 8 ]. New researches suggested non-invasive brain stimulation (NIBS), including repetitive transcranial magnetic stimulation (rTMS), transcranial direct current stimulation (tDCS), deep brain stimulation (DBS), and electroconvulsive therapy (ECT) may be a new treatment for OCD, PTSD and Ads [ 9 ]. Among these NIBS techniques, tDCS is characterized by its relatively safe, well-tolerable, low cost and convenient combination with pharmacotherapy, making it more suitable for clinical promotion and application [ 10 ]. Therefore, it is crucial and practical to determine the effect of tDCS on OCD, PTSD and ADs.

tDCS is a tool to modulate synaptic connections and induce cortical functioning by supplying a mild direct current (usually 0.5MA–2MA) over the scalp [ 10 ]. The effect of tDCS is polarity-dependent: anodal stimulation increases cortical excitability by depolarizing neurons, and cathodal stimulation inhibits cerebral excitability by hyperpolarizing neurons [ 11 ]. Additionally, parameters of tDCS such as current intensity, duration and stimulation sessions also have a significant influence on the level of excitability [ 12 , 13 ]. However, the optimal protocol of tDCS is still being explored. Researches have shown that tDCS not only modulated cortical excitability by altering the resting membrane potential during stimulation but also modified synaptic activity to produce aftereffects [ 14 ]. Therefore, it is necessary to focus on both the immediate and long-term efficacy of tDCS.

NIBS, as a treatment technology, is based on physiology and pathological mechanism of the diseases. Increasing evidence to demonstrates that OCD is associate with hyperactivation of cortical-striatum-thalamus-cortical (CSTC) circuitry [ 15 , 16 ], and several components of the circuitry such as orbitofrontal cortex (OFC), dorsolateral prefrontal cortex (DLPFC), and medial prefrontal cortex (mPFC) have been tested as targets for OCD treatment using NIBS [ 17 , 18 ]. The brain regions involved in PTSD include the amygdal, dorsal anterior cingulate cortex (dACC) and mPFC, which are responsible for fear responses in humans [ 19 , 20 ]. Moreover, DLPFC, as a core component of central executive network (CEN), is correlated with cognitive control in PTSD [ 21 ]. Although ADs involve different subtypes, they are closely related to fear responses [ 22 ]. Thus, the most consistent physiological characteristic of ADs is the overactivation of the amygdala, similar to PTSD [ 23 , 24 ]. Neuroimaging studies have also highlighted the hypoactivity of the prefrontal cortex in anxiety patients, and emphasized that the hyperactivity amygdala might be caused by inadequate inhibitory control of the prefrontal cortex [ 25 , 26 ]. As a result, the anodal target for NIBS in anxiety disorders is primarily focused on the left dorsolateral prefrontal cortex (L-DLPFC). Moreover, hypo- and hyperactivity in the left and right DLPFC is associated with emotional dysregulation and attention bias towards negative information in MDD [ 27 ]. tDCS may also be effective in alleviating symptoms of depression in these diseases. In summary, OCD, PTSD and ADs not only share fundamental clinical features but also involve similar neuropathological mechanisms, such as the amygdal and prefrontal cortex. Therefore, it is more valuable and meaningful to synthesize them in order to quantitatively analyze the effect of tDCS.

Previous meta-analysis studies amied to explore the efficacy of NIBS on specific symptoms of OCD [ 28 ], PTSD [ 29 ] and ADs [ 30 ] individually. Shu and colleagus inverstigated the efficacy of NIBS on OCD that included four tDCS studies. The authors concluded that tDCS was not superior to the sham stimulation in alleviating OCD symptoms [ 28 ]. Rebecca and colleagus did not quantitatively explore the effects of tDCS on posttraumatic core symptoms due to limitations in the number of studies. Their paper included two tDCS studies both of which suggested a significant reduction in PTSD symptoms compared to the sham tDCS [ 29 ]. Alessandra and colleagus conducted a quantitative analysis of the effectiveness of NIBS in the treatment of anxiety disorders. Their study showed that NIBS can alleviate clinical symptoms in patients with anxiety disorders, but they didn’t analyse the potency of tDCS separately [ 30 ]. Overall, on the one hand, we discover the effect of tDCS has not received enough attention, and its long-term effects are seldom noticed. On the other hand, previous meta-analysis explored the effect of tDCS on OCD, PTSD, and ADs separately instead of integrating them.

In conclusion, our study aims to conduct a quantitative analysis of existing studies on tDCS for OCD, PTSD, and ADs. We will investigate the immediate and long-term efficacy of tDCS for specific symptoms and general anxiety symptoms in these diseases. Considering that the comorbidity of anxiety and depression is up to 30–67% [ 31 ], and existing meta-analyses have already indicated that tDCS can treat major depressive episodes [ 32 ]. We will also examine the effectiveness of tDCS for depression symptoms in OCD, PTSD, and ADs. Finally, we will test the association between tDCS stimulation parameters and effect sizes using meta-analysis regression.

The present review followed the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) [ 33 ]. This meta-analysis was registered with the PROSPERO, with the registration number CRD42023418957 ( https://www.crd.york.ac.uk/PROSPERO ).

Search strategy

Four English databases including PubMed, Web of Science, Embase and the Cochrane Library, and three Chinese databases involving Chinese National Knowledge Infrastructure (CNKI), WanFang and the Chinese Biomedical Literature Database (CBM), were systematically searched articles related to the treatment of OCD, PTSD, and ADs with tDCS from May 2012 to June 5th 2024. In our search, we discovered that the first study on tDCS therapy for related disorders was published in May 2012 [ 34 ], prompting us to commence within this period. We adopted Medical Subject Headings (MeSH) or Entry Terms for “tDCS” along with relevant disorders (such as “obsessive compulsive disorder,” “posttraumatic stress disorder,” “generalized anxiety disorder,” “panic disorder,” “agoraphobia,” “specific phobia,” “social anxiety disorder”) (See Supplementary materials STable 1 ). Additionally, we manually searched the related meta-analyses of our study to identify other eligible studies.

Inclusion and exclusion criteria

Studies were included if they fulfilled the following criteria: (1) 18–70 years old; (2) clinical diagnosis of OCD, PTSD or ADs according to DSM, ICD or CCMD, and clarify the diagnostic types of anxiety disorders; (3) Unrestricted use of medication and psychological therapy; (4) randomized, sham-controlled trials using tDCS, with consistent target areas for active and sham tDCS; if the study is the randomized controlled crossover trial, the data from the first stage will be used; (5) At least one validated clinical scale as an outcome measure.

Studies were excluded if: (1) no clear criteria of clinical diagnosis; (2) Comorbid neurological diseases, current addiction, bipolar, psychotic, and neurocognitive disorders; (3) no sham tDCS as control or the target areas for active and sham tDCS were inconsistent; (4) duplicated data sets; (5) review, case-report, meta-analysis, and meeting abstracts. Furthermore, comorbid depression and anxiety disorders were not considered as criteria for exclusion.

Records screening and data extraction

Firstly, two researchers (XL, HP) independently conducted preliminary screening according to inclusion and exclusion criteria based on the research title and abstract. The records were categorized as “include,” “exclude” or “maybe”. Then, studies that could not be determined for inclusion underwent full-text reading and screening. Any conflicts during the title-abstract and full-text screening stages were resolved through discussion and reach consensus. If consensus could not be reached, the researchers would discuss with a third senior researcher. Finally, two researchers independently extracted and verified data form included literature. The following data were extracted: article indexing information, subject demographic information, tDCS treatment parameters, outcome measures, and pre- and post- treatment data, including follow-up data. If the data was unavailable in original publications, the corresponding author was contacted.

Study quality assessment

Two researchers (XL, HP) conducted independent assessments of the quality of the included studies using the Cochrane Collaboration’s Risk of Bias Tool (RoB2) [ 35 ]. This tool is structured into five bias domains, which include “the randomization process,” “intended interventions,” “missing outcome data,” “measurement of the outcome” and “selection of the reported result.” The overall risk of bias for a study depends on assessment of each individual domain. If all domains are judged to have a low risk of bias, the overall risk of bias is considered low and the study is considered to have high quality. Conversely, if at least one domain is judged to raise some concerns and not to be at high risk of bias for any domain, the overall risk of bias is considered to have some cencerns and the study is considered to have moderate quality. Furthermore, other merging estimation is considered to have a high risk. To determine the bias in the domain of “selection of the reported result,” researchers examined the registered protocol provided in the paper. Conflicts were resolved through consultation, and a third researcher was consulted if necessary.

Quantitative analysis

The data extracted from each study were quantitatively analyzed. The primary outcome measures were the change scores of pre-post treatment mean difference in disorder-specific symptoms scale and general anxiety symptoms scale. The secondary outcome measures included the change scores of before treatment to follow-up mean difference in disorder-specific symptoms scale and general anxiety symptoms scale, as well as the change scores of pre-post treatment mean difference in general depression symptoms scale. When there were two validated clinical questionnaires assessing the same outcome (e.g., anxiety symptoms: HAMA, BAI), the scale that was used more frequently in other studies was selected. The standard deviation of the change score was calculated as suggested by the Cochrane Handbook for systematic Reviews of Interventions [ 35 ], as follows:

where corr is the correlation between pre- and post-measurements variances, set at 0.5 as suggested by Follman and colleagues [ 36 ].

The analysis was performed using Stata 16.0. Using the “metan” package to calculate Hedges’g as the measure of effect size. This calculation helps correct bias due to small samples sizes [ 36 ]. Heterogeneity was assessed using Q-test and I 2 metric. Subgroup analysis by diseases was conducted to explore whether disease was the source of heterogeneity. Sensitivity analysis was performed using the “metaninf” package to test for heterogeneity caused by outliers in a study. Additionally, Egger’s regression and the funnel plot were used to analyze publication bias. Finally, meta-regression was employed to investigate the association between tDCS stimulation parameters (the number of sessions, current intensity, session duration, anode targets) and effect sizes. Among them, convert anode targets into dummy variables for regression analysis. According to the Cochrane Handbook’s recommendations, a funnel plot and meta-regression is conducted when there are at least 10 studies [ 35 ]. Due to the different features included in the studies (such as patient characteristics, stimulation parameters, scales, etc.) and the presence of varying effect sizes, the random effects model was chosen for all analyses. This model helps to account for the errors caused by sampling errors and real differences in effect sizes [ 37 , 38 ].

Study selection and characteristics

The literature search is presented in Fig. 1 . A total of 2094 records were retrieved from 7 databases, and 683 duplicate records were removed. Based on the inclusion criteria, full-text of 28 papers was retrieved, and 15 papers were ultimately included in the analysis. Among these, the study by Jafari et al. [ 39 ] and Jaber et al. [ 40 ] included subjects divided into three groups: both active tDCS groups with different current intensities (1MA, 2MA), and a sham tDCS group. For the analysis, these reports were considered as two independent studies. In addition, the report by Smits et al. [ 41 ] included two types of diseases (PTSD and ADs), Due to the lack of definitive diagnosis of ADs, we only extracted data on PTSD symptoms for analysis. The characteristics of the participants are described in Table 1 .

Flow chart of literature search.

The detailed results of the quality assessment are documented in Table 2 . Among these studies, 70.6% (12/17) of the studies were deemed to have a low risk of bias and high quality, while 23.5% (4/17) of the studies were considered to have a moderate quality. Only one study has a high risk of bias. To improve the quality of meta-analysis, the study with high-risk bias was excluded in the main text. The supplementary materials will provide the results of all studies (the result has not changed).

The main sources of bias in the studies were identified as “selection of the reported result” and “intended interventions.” In terms of selective reporting, certain studies [ 42 , 43 , 44 ] did not mention the registered protocol, making it impossible to determine if selective reporting occurred. Regarding intervention bias, studies categorized as having “some concerns” did not explicitly state whether the experimenter who applied the tDCS was aware of the purposes of the study. Moreover, the randomization design, as a secondary factor, had an impact on bias. Despite the random allocation of participants, studies conducted by Gowda [ 45 ] and Smits [ 41 ] et al. had a significant statistical difference in the sex radio between sham and tDCS group, which could potentially impact the study results.

tDCS stimulation parameters

The stimulation parameters are detailed in Table 3 . Firstly, regarding the placement of the target area, the anode was positioned on the L- DLPFC in 11 studies, while the cathode areas varied. Secondly, in terms of current intensity, it ranged from 1MA to 2MA, with 13 studies applying a current of 2MA. Moving on to stimulation sessions, 2 studies administered 5 sessions, while 10 studies included 10 sessions. Finally, with regards to session duration, 12 studies had a duration of 20 min, while the remaining studies had a duration of 30 min.

Analysis of the primary outcome

Disorder-specific symptoms.

A total of 15 studies fulfilled the eligibility criteria for the primary outcome with disorder-specific symptoms, including 643 participants (See supplementary materials STable 2 – 4 ). The results of meta-ananlysis showed that tDCS reduced the specific symptoms in OCD, PTSD, and ADs, with a high effect size (SMD = −0.73, 95% CI: −1.09 to −0.37; Z  = −3.960, p  < 0.001) and a high heterogeneity (I 2  = 77.8%, p  < 0.001) (Fig. 2A ).

A Immediate effect size of tDCS on disorder-specific symptoms. B Immediate effect size of tDCS on general anxiety symptoms. C Long-term effect size of tDCS on disorder-specific symptoms. D Long-term effect size of tDCS on general anxiety symptoms. CI confidence interval.

Subgroup analysis indicated that tDCS effectively improved the specific symptoms in SAD, GAD, and OCD (SMD SAD  = −2.27, 95% CI: −2.97 to −1.57, I 2  = 0%, p  > 0.05; SMD GAD  = −0.61, 95% CI: −1.03 to −0.19, I 2  = 0%, p  > 0.05; SMD OCD  = −0.55, 95% CI: −1.00 to −0.09, I 2  = 77.1%, p  < 0.001). Conversely, tDCS couldn’t alleviate specific symptoms of PD and PTSD (SMD PD  = 0.27, 95% CI: −0.45 to 0.99, I 2  = 0%, p  < 0.001; SMD PTSD  = −0.90, 95% CI: −1.82 to 0.03, I 2  = 73.0%, p  > 0.05).

Sensitivity test results showed that no outliers from any study influenced the overall results. Nevertheless, in terms of publication bias, the funnel plot indicated symmetry (Fig. 3A ) and Egger’s regression test suggested no significant statistical difference ( t  = −1.03, p  = 0.323).

A Immediate efficacy for disorder-specific symptoms. B Immediate efficacy for general anxiety symptoms. C Long-term efficacy for disorder-specific symptoms.

General anxiety symptoms

There were 10 studies involving 422 subjects that reported the general anxiety symptoms. The results of meta-analysis suggested that tDCS reduced the severity of general anxiety symptoms in OCD, PTSD and ADs, with a high effect size (SMD = −0.75; 95% CI: −1.23 to −0.26; Z  = −2.999, p  < 0.01). Q-statistics and I 2 indicated that the included studies had a high heterogeneity (I 2  = 80.7%, p  < 0.001) (Fig. 2B ).

The results of subgroup analysis indicated that tDCS alleviated general anxiety symptoms in SAD, PTSD and OCD (SMD SAD  = −2.29, 95% CI: −3.59 to −0.98, I 2  = 69.5%, p  > 0.05; SMD PTSD  = −0.80, 95% CI: −1.51 to −0.10, I 2  = 0%, p  < 0.001; SMD OCD  = −0.50, 95% CI: −0.98 to −0.01; I 2  = 73.4%, p  < 0.01). However, tDCS had no significant impact on general anxiety symptoms in PD (SMD = 0.24, 95% CI: −0.48 to 0.96, I 2  = 0%, p  < 0.001).

The results of the sensitivity analysis indicated that omitting any study, the results of the remaining studies were consistent with the original results. The funnel plot may indicate the presence of publication bias (Fig. 3B ), although Egger’s regression test did not show statistical significance ( t  = −0.67, p  = 0.522).

Analysis of the secondary outcome

Follow-up of disorder-specific symptoms.

A total of 13 studies reported the follow-up results. Among these, only one study recorded data for one-week follow-up [ 46 ], while the follow-up periods in other studies were longer or close to one month, our study focuses on the long-term effects of tDCS, so the study with a one-week follow-up was excluded. The meta-analysis of the remaining 12 studies, which involving 460 subjects, showed that tDCS had a long-term effect on disorder-specific symptoms in OCD, PTSD, and ADs, with a moderate effect size (SMD = −0.60; 95% CI: −1.04 to −0.16; Z  = −2.650, p  < 0.01) and a high heterogeneity (I 2  = 79.7%, p  < 0.001) (Fig. 2C ).

Subgroup analysis showed that tDCS provide a long-term effect in alleviating the specific symptoms in SAD and OCD (SMD SAD  = −2.20, 95% CI: −2.95 to −1.46, I 2  = 0.0%, p  > 0.05; SMD OCD  = −0.39, 95% CI: −0.68 to −0.09, I 2  = 22.3%, p  > 0.05). However, tDCS did not provide a long-term effect in alleviating the specific symptoms in PTSD (SMD = −0.45, 95% CI: −1.49 to 0.60, I 2  = 87.9%, p  < 0.001).

The results of the sensitivity analysis indicated that omitting any study, the results of the remaining studies were consistent with the original results. Meanwhile, the funnel plot (Fig. 3C ) and Egger’s regression test ( t  = −3.19, p  < 0.05) indicated significant publication bias.

Follow-up of general anxiety symptoms

Follow-up results of general anxiety symptoms were recorded in 7 studies. The meta-analysis of the results suggested that tDCS does not provide a long-term effect in reducing the severity of general anxiety symptoms in OCD, PTSD, and ADs (SMD = −0.30; 95% CI: −0.68 to 0.09; Z  = −1.523, p  > 0.05), with a high heterogeneity (I 2  = 53.3%, p  < 0.05).

The results of sensitivity analysis showed the study of Aksu et al. [ 47 ] had a strong heterogeneity. After excluding this study, the results suggested that tDCS has a long-term effectiveness in reducing the severity of general anxiety symptoms in OCD, PTSD, and ADs (SMD = −0.41; 95% CI: −0.78 to −0.03; Z  = −2.140, p  < 0.05), with a moderate heterogeneity (I 2  = 43.4%, p  = 0.116) (Fig. 2D ). Subgroup analysis showed that tDCS provided a long-term effect in alleviating the general anxiety symptoms in PTSD (SMD = −0.98, 95% CI: −1.70 to −0.26, I 2  = 0%, p  < 0.001) and has no long-term effect in alleviating the general anxiety symptoms in OCD (SMD = −0.28, 95% CI: −0.63 to 0.07, I 2  = 26.5%, p  > 0.05). Due to the limited number of studies, only Egger’s regression test was conducted, and the results indicated no significant publication bias ( t  = −1.10, p  > 0.05).

General depression symptoms

A total of 9 studies involving 310 subjects have reported the results of general depression scales. The meta-analysis of results revealed that tDCS effectively improved the general depression symptoms in OCD, PTSD, and ADs (SMD = −0.70, 95% CI: −1.09 to −0.31; Z  = −3.487, p  < 0.001), with a high heterogeneity (I 2  = 62.1%, p  < 0.01). Subgroup analysis showed that tDCS could improve the general depression symptoms in SAD, PTSD, OCD (SMD SAD  = −1.07, 95% CI: −2.06 to −0.09; I 2  = 65.2%, p  > 0.05; SMD PTSD  = −1.14, 95% CI: −1.88 to −0.41, I 2  = 0%, p  < 0.001; SMD OCD  = −0.62, 95% CI: −1.13 to −0.12, I 2  = 60.6%, p  > 0.05), while it did not significantly reduce the severity of general depression symptoms in PD (SMD = 0.05, 95% CI: −0.66 to 0.77, I 2  = 0%, p  < 0.001).

Sensitivity test results showed that no outliers from any study influenced the overall results. The Egger’s regression test ( t  = −2.85, p  < 0.05) indicated the presence of some publication bias.

Meta-regression analysis

Meta-regression analysis was conducted on outcome measures that included at least 10 studies. The results showed that tDCS stimulation parameters such as the number of sessions, current intensity, session duration, and target location of the anode did not explain the heterogeneity. Statistical characteristics for each covariate are recorded in Table 4 .

The meta-analysis aimed to investigate the impact of tDCS in reducing disorder-specific symptoms, general anxiety, and depression symptoms for patients with OCD, PTSD and ADs. This study also explored the effects of different tDCS parameters on effectiveness. The results indicated that tDCS could immediately improve the clinical symptoms of OCD, PTSD, and ADs, with a high effect size. It is worth noting that the effect of tDCS on disease-specific and general anxiety symptoms can be maintained for up to one month, with a moderate effect size. Moreover, the tDCS parameters, including the number of sesssions, current intensity, session duration and target location of the anode did not have a significant influence on efficacy.

Immediate effects of tDCS on clinical symptoms of diseases

Based on the immediate therapeutic effects of tDCS on specific symptoms, general anxiety symptoms, and general depression symptoms of PTSD, OCD and ADs, we found that the effects of tDCS on different diseases varies.

First, only one randomized sham-controlled study about PD [ 47 ], Contrary to the researchers’ hypotheses, the results indicates that tDCS does not improve clinical outcomes. The researchers believe this may be due to the high placebo response in randomized controlled trials of anxiety disorders. Additionally, the clinical severity of PD included in the study is relatively low, which can lead to a higher placebo response and influence the results [ 47 ].

Secondly, our results suggest that tDCS has the potential to improve clinical symptoms of GAD and SAD with moderate and high effect sizes, respectively, which is consistent with the latest review of treatments for anxiety disorders [ 48 ]. Our study includes 2 studies on tDCS for GAD and 2 studies on tDCS for SAD, all with the anode placed at the L-DLPFC, further supporting that the L-DLPFC is an effective target for tDCS treatment of ADs. On the one hand, the excitatory stimulation of the L-DLPFC may upregulate the positive response to positive emotional stimuli and downregulate the negative response to emotional stimuli, enhancing emotional regulation ability [ 49 ]; On the other hand, tDCS may increase the functional connectivity between the DLPFC and limbic network, including the amygdala, thereby improving attention control and reducing hypersensitivity of the amygdala to threat stimuli [ 25 , 50 ]. These processes are related to the core symptoms of anxiety disorders (fear, avoidance). In fact, neuroimaging studies have shown a negative correlation between DLPFC activity and anxiety [ 51 ].

Thirdly, our meta-analysis included three studies on tDCS treatment for PTSD, and the results suggested that tDCS did not improve specific symptoms of PTSD [ 41 , 52 , 53 ]. We cannot conclude the efficacy of tDCS on general anxiety and depressive symptoms in PTSD due to limited studies. The three studies showed variations in the severity of the PTSD, tDCS treatment protocols, and treatment outcomes. Therefore, we believe that the efficacy of tDCS may differ across various severities of PTSD. In addition, the target area, number of sessions, and interval between tDCS treatments may also influence effectiveness. Future research should continue to expand on existing studies to clarify the efficacy of tDCS for PTSD.

Long-term effects of tDCS on clinical symptoms of diseases

It is worth noting that as a novel result of this meta-analysis, we discovered that tDCS can improve specific symptoms and general anxiety symptoms of PTSD, OCD, and ADs for up to one month.

We believe that periodic tDCS may induce the late LTP-like plasticity. Long term potentiation (LTP), involves to the enduring functional enhancement of synaptic connections, or structural modification of neuronal connections [ 54 ]. It is divided into Early LTP (E-LTP) and Late LTP (L-LTP) depending on whether excitability alterations last for more than 3 h [ 55 ]. when the periodic tDCS protocols induce neuroplastic changes lasting for several days or weeks, this is referred to as L-LTP. L-LTP may be a candidate mechanism for long-term memory formation [ 56 ]. E-LTP relies on the activation of calcium-dependent kinases [ 57 ]. L-LTP requires gene expression and protein synthesis to achieve changes in synaptic strength, and also involves modifications to the activity of AMPA and NMDA receptors [ 58 , 59 ].

Late LTP-Like plasticity might be the mechanism through which tDCS produces long-term effects. Additionally, studies have shown that the interval between tDCS sessions plays a crucial role in L-LTP [ 59 ], and future studies should consider controlling this variable to investigate the optimal treatment regimen with tDCS.

When interpreting the research findings, it is important to consider the limitations of this study comprehensively. Firstly, due to differences in demographic data, assessment tools, and tDCS treatment parameters, most of the results showed quite heterogeneity. While we attempted to use a random effect model and performed meta-regression, it is crucial to acknowledge this as a significant limitation of our findings. However, it should also be noted that I 2 may be overestimated in a small meta-analyses [ 60 ]. Secondly, the well-known high placebo response in tDCS must be taken into account [ 61 ], highlighting the importance of a blind procedure in study design. Unfortunately, due to the limitation of the number of studies, we were unable to strictly control this variable in our study. Thirdly, the number of randomized controlled studies on tDCS for OCD, PTSD, and ADs is limited, so we are unable to control for comorbidities or other interventions. In the future, further research should be conducted to investigate the immediate and long-term efficacy of tDCS in these disorders, in order to provide additional evidence to clarify of the efficacy of tDCS and elucidate the underlying pathological mechanisms of these diseases.

tDCS improves the clinical symptoms of OCD, PTSD and ADs immediately, and the efficacy can last for 1 month. tDCS can serve as a non-invasive brain stimulation technology for treating these disorders, and the therapeutic effects can be maintained for a period of time.

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This work was supported by the National Natural Science Foundation of China (82271546, 82101625); National Key Research and Development Program of China (2023YFC2506201); Fund Program for the Scientific Activities of Selected Returned Overseas Professionals in Shanxi Province (20240041); Special fund for Science and Technology Innovation Teams of Shanxi Province (202304051001049).

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Luxin Xie, Peina Hu, Zhenglong Guo, Miao Chen, Xiao Wang, Xinzhe Du, Yue Li, Wentao Zhao & Sha Liu

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LXX: conceptualization, methodology, software, writing—original draft. PNH: methodology, software, writing—original draft. ZLG: methodology, supervision. MC: methodology, software, validation. XW: methodology, software. XZD: software, supervision, validation. YL: methodology, visualization. BC: visualization, review & editing. JHZ: visualization, review & editing. WTZ: conceptualization, writing—review & editing. SL: conceptualization, writing—review & editing.

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Supplementary prism-checklist, supplementary materials, sfigure 1: forest plots of the effect size of tdcs on disorder-specific symptoms (a and b)., sfigure 2: funnel plots for disorder-specific symptoms (a and b)., stable 1: specific query in different databases., stable 2: the raw data of specific-disorder sympotoms., stable 3: the raw data of general anxiety sympotoms., stable 4: the raw data of general anxiety sympotoms., rights and permissions.

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Xie, L., Hu, P., Guo, Z. et al. Immediate and long-term efficacy of transcranial direct current stimulation (tCDS) in obsessive-compulsive disorder, posttraumatic stress disorder and anxiety disorders: a systematic review and meta-analysis. Transl Psychiatry 14 , 343 (2024). https://doi.org/10.1038/s41398-024-03053-0

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Systematic and other reviews: criteria and complexities

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Review articles can be extremely valuable. They synthesize information for readers, often provide clarity and valuable insights into a topic; and good review articles tend to be cited frequently. Review articles do not require Institutional Review Board (IRB) approval if the data reviewed are public (including private and government databases) and if the articles reviewed have received IRB approval previously. However, some institutions require IRB review and exemption for review articles. So, authors should be familiar with their institution’s policy. In assessing and interpreting review articles, it is important to understand the article’s methodology, scholarly purpose and credibility. Many readers, and some journal reviewers, are not aware that there are different kinds of review articles with different definitions, criteria and academic impact [ 1 ]. In order to understand the importance and potential application of a review article, it is valuable for readers and reviewers to be able to classify review articles correctly.

Systematic reviews

Authors often submit articles that include the term “systematic” in the title without realizing that that term requires strict adherence to specific criteria. A systematic review follows explicit methodology to answer a well-defined research question by searching the literature comprehensively, evaluating the quantity and quality of research evidence rigorously, and analyzing the evidence to synthesize an answer to the research question. The evidence gathered in systematic reviews can be qualitative or quantitative. However, if adequate and comparable quantitative data are available then a meta-analysis can be performed to assess the weighted and summarized effect size of the studies included. Depending on the research question and the data collected, systematic reviews may or may not include quantitative meta-analyses; however, meta-analyses should be performed in the setting of a systematic review to ensure that all of the appropriate data were accessed. The components of a systematic review can be found in an important article by Moher et al. published in 2009 that defined requirements for systematic reviews and meta-analyses [ 2 ].

In order to optimize reporting of meta-analyses, an international group developed the Quality of Reporting of Meta-Analyses (QUOROM) statement at a meeting in 1996 that led to publication of the QUOROM statement in 1999 [ 3 ]. Moher et al. revised that document and re-named the guidelines the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). The PRISMA statement included both meta-analyses and systematic reviews, and the authors incorporated definitions established by the Cochrane Collaboration [ 4 ]. The PRISMA statement established the current standard for systematic reviews. To qualify as a systematic review, the methods section should acknowledge use of the PRISMA guidelines, and all PRISMA components should be incorporated strictly in all facets of the paper from the research question to the discussion. The PRISMA statement includes a checklist of 27 items that must be included when reporting a systematic review or meta-analysis [ 2 ]. A downloadable version of this checklist can be used by authors, reviewers, and journal editorial staff to ensure compliance with recommended components [ 5 ]. All 27 will not be listed in this brief editorial (although authors and reviewers are encouraged to consult the article by Moher et al. and familiarize themselves with all items), but a few will be highlighted.

The research question, as reflected in the title, should be a hypothesis-based specific research inquiry. The introduction must describe the rationale for the review and provide a specific goal or set of goals to be addressed. The type of systematic review, according to the Cochrane Collaboration, is based on the research question being asked and may assess diagnostic test accuracy, review prognostic studies evidence, evaluate intervention effect, scrutinize research methodology, or summarize qualitative evidence [ 6 ].

In the methods section, the participants, interventions, comparisons, outcomes and study design (PICOS) must be put forward. In addition to mentioning compliance with PRISMA, the methods section should state whether a review protocol exists and, if so, where it can be accessed (including a registration number). Systematic reviews are eligible for registration in the International Prospective Register of Systematic Reviews (PROSPERO) as established at the University of York (York, UK). When PROSPERO is used (it is available but not required for systematic reviews), registration should occur at the initial protocol stage of the review, and the final paper should direct to the information in the register. The methods section also must include specific study characteristics including databases used, years considered, languages of articles included, specific inclusion and exclusion criteria for studies; and rationale for each criterion must be included. Which individuals specifically performed searches should be noted. Electronic search strategy (with a full description of at least one electronic search strategy sufficient to allow replication of the search), process for article selection, data variables sought, assumptions and simplifications, methods for assessing bias risk of each individual study (such as selective reporting in individual studies) and utilization of this information in data synthesis, principal summary measures (risk ratio, hazard ratio, difference in means, etc.), methods of data management and combining study results, outcome level assessment, and other information should be reported.

The results section should include the number of studies identified, screened, evaluated for eligibility (including rationale for exclusion), and those included in the final synthesis. A PRISMA flow diagram should be included to provide this information succinctly [ 7 ]. The results also should include the study characteristics, study results, risk of bias within and across studies, and a qualitative or quantitative synthesis of the results of the included studies. This level of rigor in acquiring and evaluating the evidence of each individual study is one of the criteria that distinguishes systematic reviews from other categories. If the systematic review involves studies with paired samples and quantitative data, a summary of data should be provided for each intervention group along with effect estimates and confidence intervals for all outcomes of each study. If a meta-analysis is performed, then synthesized effect size should be reported with confidence intervals and measures of consistency (i.e. – data heterogeneity such as I 2 ) for each meta-analysis, and assessment of bias risk across studies. A forest plot, which provides a graphical presentation of the meta-analysis results, should be included.

The discussion section should summarize the main findings commenting on the strength of evidence for each outcome, as well as relevance to healthcare providers, policymakers and other key stake-holders; limitations of the study and outcomes; and conclusions highlighting the interpretation of results in the context of other research, and implications for future research.

Without adhering to of all of these criteria and the others listed in the PRISMA statement and checklist, the review does not qualify to be classified as “systematic”.

Meta-analyses

Meta-analyses, when feasible based on available and comparable quantitative data, supplement a systematic review evaluation, by adding a secondary statistical analysis of the pooled weighted outcomes of similar studies. This adds a level of objectivity in the synthesis of the review’s findings. Meta-analyses are appropriate when at least 2 individual studies contain paired samples (experimental group and control group) and provide quantitative outcome data and sample size. Studies that lack a control group may over-estimate the effect size of the experimental intervention or condition being studied and are not ideal for meta-analyses [ 8 ]. It also should be remembered that the conclusions of a meta-analysis are only as valid as the data on which the analysis is based. If the articles included are flawed, then the conclusions of the meta-analysis also may be flawed. Systematic reviews and meta-analyses are the most rigorous categories of review.

Other types of reviews

Mixed methods reviews.

Systematic reviews typically contain a single type of data, either qualitative or quantitative; however, mixed methods reviews bring together a combination of data types or study types. This approach may be utilized when quantitative data, in the setting of an intervention study, only provide a narrow perspective of the efficacy or effectiveness of the intervention. The addition of qualitative data or qualitative studies may provide a more complete picture of the knowledge, attitudes, and behaviors of clinicians, patients or researchers regarding that intervention. This type of review could involve collecting either the quantitative or the qualitative data using systematic review methodology, but often the qualitative data are gathered using a convenience sampling. Many qualitative studies provide useful insights into clinical management and/or implementation of research interventions; and incorporating them into a mixed methods review may provide valuable perspective on a wide range of literature. Mixed methods reviews are not necessarily systematic in nature; however, authors conducting mixed methods reviews should follow systematic review methodology, when possible.

Literature and narrative reviews

Literature reviews include peer-reviewed original research, systematic reviews, and meta-analyses, but also may include conference abstracts, books, graduate degree theses, and other non-peer reviewed publications. The methods used to identify and evaluate studies should be specified, but they are less rigorous and comprehensive than those required for systematic reviews. Literature reviews can evaluate a broad topic but do not specifically articulate a specific question, nor do they synthesize the results of included studies rigorously. Like mixed method reviews, they provide an overview of published information on the topic, although they may be less comprehensive than integrative reviews; and, unlike systematic reviews, they do not need to support evidence-based clinical or research practices, or highlight high-quality evidence for the reader. Narrative reviews are similar to literature reviews and evaluate the same scope of literature. The terms sometimes are used interchangeably, and author bias in article selection and data interpretation is a potential concern in literature and narrative reviews.

Umbrella reviews

An umbrella review integrates previously published, high-quality reviews such as systematic reviews and meta-analyses. Its purpose is to synthesize information in previously published systematic reviews and meta-analyses into one convenient paper.

Rapid review

A rapid review uses systematic review methodology to evaluate existing research. It provides a quick synthesis of evidence and is used most commonly to assist in emergent decision-making such as that required to determine whether COVID-19 vaccines should receive emergent approval.

Scoping, mapping, and systematized reviews

If literature has not been reviewed comprehensively in a specific subject that is varied and complex, a mapping review (also called scoping review) may be useful to organize initial understanding of the topic and its available literature. While mapping reviews may be helpful in crystallizing research findings and may be published, they are particularly useful in helping to determine whether a topic is amenable to systematic review, and to help organize and direct the approach of the systematic review or other reviews of the subject. Systematized reviews are used most commonly by students. The systematized review provides initial assessment of a topic that is potentially appropriate for a systematic review, but a systematized review does not meet the rigorous criteria of a systematic review and has substantially more limited value. Additional types of reviews exist including critical review, state-of-the-art review, and others.

Reviews can be invaluable; but they also can be misleading. Systematic reviews and meta-analyses provide readers with the greatest confidence that rigorous efforts have attempted to eliminate bias and ensure validity, but even they have limitations based upon the strengths and weaknesses of the literature that they have assessed (and the skill and objectivity with which the authors have executed the review). Risks of bias, incomplete information and misinformation increase as the rigor of review methodology decreases. While review articles may summarize research related to a topic for readers, non-systematic reviews lack the rigor to answer adequately hypothesis-driven research questions that can influence evidence-based practice. Journal authors, reviewers, editorial staff, and should be cognizant of the strengths and weaknesses of review methodology and should consider them carefully as they assess the value of published review articles, particularly as they determine whether the information presented should alter their patient care.

Authors’ contributions

The author(s) read and approved the final manuscript.

Declarations

The authors declare no competing interests.

This article is co-published in the following journals: Journal of Voice, Otology & Neurotology, Ear, Nose and Throat Journal, Journal of Laryngology and Otology, Operative Techniques in Otolaryngology – Head and Neck Surgery, Head & Neck, International Journal of Pediatric Otorhinolaryngology, Journal of Neurological Surgery Part B: Skull Base, Otolaryngology – Head and Neck Surgery, World Journal of Otorhinolaryngology – Head and Neck Surgery, The Laryngoscope, American Journal of Rhinology & Allergy, Annals of Otology, Rhinology & Laryngology, Clinical Otolaryngology, American Journal of Otolaryngology, Laryngoscope Investigative Otolaryngology.

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• Open access
• Published: 21 August 2024

Pediatric head injury guideline use in Sweden: a cross-sectional survey on determinants for successful implementation of a clinical practice guideline

• Fredrik Wickbom 1 , 2 ,
• William Berghog 1 ,
• Susanne Bernhardsson 3 , 4 , 5 ,
• Linda Persson 6 ,
• Stefan Kunkel 7 &
• Johan Undén 1 , 2  

BMC Health Services Research volume  24 , Article number:  965 ( 2024 ) Cite this article

75 Accesses

Metrics details

The Scandinavian Neurotrauma Committee guideline (SNC-16) was developed and published in 2016, to aid clinicians in management of pediatric head injuries in Scandinavian emergency departments (ED). The objective of this study was to explore determinants for use of the SNC-16 guideline by Swedish ED physicians.

This is a nationwide, cross-sectional, web-based survey in Sweden. Using modified snowball sampling, physicians managing children in the ED were invited via e-mail to complete the validated Clinician Guideline Determinants Questionnaire between February and May, 2023. Baseline data, data on enablers and barriers for use of the SNC-16 guideline, and preferred routes for implementation and access of guidelines in general were collected and analyzed descriptively and exploratory with Chi-square and Fisher's tests.

Of 595 invitations, 198 emergency physicians completed the survey (effective response rate 33.3%). There was a high reported use of the SNC-16 guideline (149/195; 76.4%) and a strong belief in its benefits for the patients (188/197; 95.4% agreement). Respondents generally agreed with the guideline's content (187/197; 94.9%) and found it easy to use and navigate (188/197; 95.4%). Some respondents (53/197; 26.9%) perceived a lack of organizational support needed to use the guideline. Implementation tools may be improved as only 58.9% (116/197) agreed that the guideline includes such. Only 37.6% (74/197) of the respondents agreed that the guideline clearly describes the underlying evidence supporting the recommendation. Most respondents prefer to consult colleagues (178/198; 89.9%) and guidelines (149/198; 75.3%) to gain knowledge to guide clinical decision making. Four types of enablers for guideline use emerged from free-text answers: ease of use and implementation, alignment with local guidelines and practice, advantages for stakeholders, and practicality and accessibility. Barriers for guideline use were manifested as: organizational challenges, medical concerns , and practical concerns.

Conclusions

The findings suggest high self-reported use of the SNC-16 guideline among Swedish ED physicians. In updated versions of the guideline, focus on improving implementation tools and descriptions of the underlying evidence may further facilitate adoption and adherence. Measures to improve organizational support for guideline use and involvement of patient representatives should also be considered.

Peer Review reports

Contributions to the literature

The pediatric Scandinavian Neurotrauma Committee head injury guideline from 2016 seems well known and well used by Swedish emergency department physicians, despite lack of formal implementation.

The study identified guideline implementation determinants that need to be addressed in both future guideline versions and in implementation strategies.

This study contributes reference data for the Clinician Guideline Determinants Questionnaire; a novel, validated tool for assessment of determinants for guideline use, with different results compared to previous reports utilizing the questionnaire.

Head trauma is a common cause to seek emergency department (ED) care among children in Sweden. In 2022, over 33,000 cases of head injury were registered in Sweden in children 0–17 years of age, according to the Swedish National Board of Health and Welfare [ 1 ]. Of these, 22.3% were diagnosed with an intracranial injury of varying severity (including concussion), yielding an overall incidence of 1521/100 000 patients with head injuries and an incidence of 340/100 000 patients with intracranial injury. Mild traumatic brain injury (mTBI) constitutes more than 80% of pediatric TBI cases globally [ 2 ]. Most of these injured children will recover without the need for acute intervention, e.g., neurosurgery or intensive care admission [ 2 , 3 , 4 , 5 ].

Cranial computed tomography (CT) utilizes ionizing radiation for imaging of the brain and is a valuable tool for excluding significant intracranial injuries, ordered in 4% of children with isolated head trauma in southern Sweden [ 6 ]. Radiation exposure in early life entails a risk of malignancy development later in life, and the selection of patients with mTBI for neuroimaging poses a clinical challenge [ 5 , 7 , 8 , 9 ]. Structured in-hospital observation is considered equally effective, although this is associated with higher resource use [ 10 , 11 ]. In Sweden (and similar to other countries), it is often junior physicians who initially manage these children, following a diverse range of local guidelines (or no guideline), resulting in an unstandardized approach to pediatric TBI on a national level [ 12 , 13 ].

The Scandinavian Neurotrauma Committee has recently developed a clinical practice guideline addressing the initial management of mTBI in children (SNC-16 guideline) in Scandinavia [ 14 ]. It was published in 2016 and has since then been passively disseminated into more than 50% of the Swedish emergency hospitals’ management routines [ 13 ]. Although validated in other settings, the SNC-16 guideline has not been validated in the Scandinavian population [ 15 , 16 ]. The SNC-16 guideline for managing patients with mTBI has been developed to help healthcare providers make informed management decisions. To assess the risk of intracranial injury, various factors such as clinical signs and symptoms (e.g., loss of consciousness, amnesia, neurological deficits) and current state of consciousness are considered in the guideline. If a patient's clinical status falls within the low-risk criteria, a CT scan or prolonged structured observation may be deemed unnecessary [ 14 ].

The process of clinically adapting research-based knowledge is widely acknowledged as intricate and non-self-regulating [ 17 , 18 , 19 ]. Clinical practice guidelines are considered valuable tools for integrating the latest medical evidence into clinical practice [ 20 , 21 ]. By identifying existing barriers and facilitators that influence the use of specific guidelines, it may be possible to tailor an implementation process and facilitate the uptake of a guideline into clinical settings and ensure adequate compliance [ 19 , 22 , 23 ].

In 2019, the Clinician Guideline Determinants Questionnaire (CGDQ) was developed and published by Gagliardi et al. [ 24 ]. This tool serves the purpose of providing a comprehensive and validated instrument for addressing factors relevant for the use or non-use of a specific guideline from a clinician's perspective. Knowledge about determinants for use and non-use specific for the SNC-16 guideline may support an implementation process and increase adherence to evidence-based practices in managing pediatric head trauma in Sweden. It may also give important information in future updates of the guideline.

The primary objective of this study was to identify barriers and enablers affecting use of the SNC-16 guideline by physicians in Sweden. Knowledge about these determinants is important as it allows development of tailored interventions in forthcoming implementation processes with the intention to promote uptake of research findings in routine care [ 24 ]. This study is part of a series of studies which embraces validation, development, and implementation of the SNC-16 guideline in Scandinavia.

Study design

This is a cross-sectional observational study in Sweden. Collection of data was performed using a validated questionnaire for implementation research [ 24 ]. Respondents were asked to assess the SNC-16 guideline based on the structured questions in the questionnaire. Reporting follows STROBE guidelines for cross-sectional studies (Additional file 1) [ 25 ]. An ethical advisory opinion was granted by the Swedish Ethical Review Authority (Dnr 2020 – 02 693).

The survey was sent to physicians in Swedish EDs of varying sizes nationwide, in which head trauma in pediatric patients is managed. Data were collected during February 23 to May 8, 2023.

Participants

Physicians from various medical specialties who regularly, at their own discretion, work in the ED of a Swedish hospital and assess pediatric acute head trauma, were included. Respondents not fulfilling the above criteria were excluded.

Potential participants were invited by an e-mail containing an information text and a link to the questionnaire. The initial e-mail recipient list of potential respondents was based on three different e-mail collection strategies: 1) a list of suggested respondents from a previous study, investigating management of pediatric TBI in Sweden at an organizational level [ 13 ]; 2) new e-mails to ED managers with a request to send us e-mail addresses to ED physicians working with pediatric mTBI in their ED (as the list from 2022 may contain irrelevant recipients or old e-mail addresses); and 3) screening of e-mail recipient lists accessible for our research team (identifying physicians in the department of general surgery in the Region of Halland, physicians in the department of emergency medicine in the Region of Halland and interns employed in the Region of Halland, Sweden). Only potential e-mail recipients suggested from a hospital that managed children with pediatric head trauma were included when extracting the e-mail list, drawn from the 66 hospitals included in the 2022 paper (370 e-mail addresses).

In summary, the final e-mail recipient list in the first block contained 502 unique e-mail addresses to potential respondents (Fig.  1 ). Non-responders were sent a total of five reminders during the time for data collection.

Flowchart describing structure for collection of the final data set

Before completing the survey, participants were asked to contribute with e-mail addresses to additional colleagues in their hospital or neighboring hospitals who they believed fulfilled the above inclusion criteria. Respondents not fulfilling the inclusion criteria were given the option to decline participation but still contribute with e-mail addresses to suitable colleagues. New e-mail addresses were added in blocks and generated in total five consecutive groups with new e-mail addresses to whom the survey was distributed. With this modified snowball sampling method, it was possible to control response rates. The study size was reached when no more new e-mail addresses were added by respondents with the snowball method, and no more non-respondents answered the survey despite multiple reminders. Respondents were pseudonymized at analysis and no patient data was recorded.

Respondents are by definition fluent in both Swedish and English as this is a criterion for admission to medical training in Swedish universities and hospitals. The medical literature in Sweden is also predominately in English.

The Clinician Guideline Determinants Questionnaire (CGDQ) was used for data collection [ 24 ]. It is a validated instrument for preparing and evaluating implementation of clinical practice guidelines. The CGDQ includes four sections exploring: 1) clinician demographic and background information; 2) attitudes to known determinants of guideline use; 3) open-ended items on additional determinants; and 4) a section examining preferred ways of distribution, access, and character of a guideline. The CGDQ was transcripted unchanged from the original version and presented in English in a digital questionnaire in the web-based survey system EsMaker (Entergate AB). As respondents have a high knowledge of the English language, we judged the risks associated with a translation of the questionnaire to Swedish greater than the risk that respondents would not understand the questions. Three questions exploring what size and type of hospital the respondent worked in, type of patients (children/adults/both) they managed, and their familiarity with assessing children with head injury were added to the background information section by the authors. The SNC-16 flow chart, a link to the original publication, and a link to an article in the Swedish medical journal Läkartidningen were presented at the beginning of the questionnaire [ 14 , 26 ]. The text “SNC-16 guideline” was inserted in the questionnaire where stated, “name guideline”. Some items have been truncated to improve readability in the results section of this paper, with a reference to the full questionnaire and complete items in Additional file 2.

To minimize the risk for introducing selection bias, purposive sampling was used to include respondents from varying parts of Sweden and from varying hospital sizes, and including both junior and senior physicians, when compiling the initial respondent mailing list.

Data analysis

Reported data are categorical nominal/dichotomous or categorical ordinal (on a 7-step Likert scale, including response option “not sure”), or in free text. Responses to categorical nominal items are summarized and presented as frequencies and percentages. Variables that are reported on an ordinal 7-step Likert scale were dichotomized into “disagree” if Likert response 1–4 or unsure, and into “agree” if Likert response 5–7. The unmerged response distribution is shown in Additional file 3. Results are presented for the four sections in the applied implementation tool (CGDQ). Merging of categories was performed if there were few responses in a response category.

Background data on respondents are presented descriptively for a) gender, b) career stage (as found most appropriate by the respondent), c) medical specialty, d) hospital category (local hospital, regional hospital, university hospital or children’s hospital – with local and regional merged as small hospitals and university and children’s as large), e) region in Sweden, f) managing only children or both children and adults, g) familiarity with assessing children with head injury (categorized as “daily” + “several times a week” = regularly; “1–3 times/month” = seldom; “5–10 times/year” + “1–4 times/year” + “less than once a year” = rarely), h) have participated in the development of one or more guidelines, i) belief in clinical benefit of guidelines, and j) actual use of SNC-16 guideline.

Frequencies and percentages for "agree” and “disagree” for determinants in Sect. 2 of the survey were calculated. The authors decided to perform further analysis on a subset of factors from the clinician and guideline specific determinants in Sect. 2, aiming to explore possible associations between determinants and background factors. The subset comprised six variables selected by the authors after reviewing initial results and considered most salient to grasp the respondent’s thoughts on the guideline and their knowledge about the relevant clinical condition, with the most clinically relevant imprint. Authors decided to not test all items as it would entail an unjustified risk for significant results by chance. Chi-square test, or Fisher’s exact test when appropriate, was used to assess associations.

The free-text responses obtained from questions 3.1 to 3.4 (additional file 2) were independently categorized into types of barriers and enablers by two of the authors (FW, WB) and then compiled in consensus.

The first invitation e-mail was sent on February 23, 2023. The final reminder was sent on April 20, 2023. Respondents suggested 93 additional unique potential respondents, resulting in invitations also sent to these individuals. In this group, 43 participants opened the e-mail and participated in the survey, yielding a response rate in the snowball sample group of 46.2%. The total response rate was 43.4% (258/595; opens and responds to request) with an effective response rate for analysable respondents of 33.3% (198/595) (Fig.  1 ).

Background information

The 198 responding physicians from 42 unique EDs had varying clinical experience, in a span from early career interns (14.1%; 28/198), mid-career residents (48.5%; 96/198), to late career consultants (37.4%; 74/198). The most common specialties represented were general surgery (52.0%; 103/198) and emergency medicine (31.8%; 63/198). A majority (82.3%; 163/198) of the respondents worked in small (local or regional hospitals) compared to 17.7% ( n  = 35) in large (university or children’s) hospitals. There was a high degree of familiarity with the SNC-16 guideline, as 84.3% (166/197) had “read all or some of the guideline on multiple occasions” and only 8.1% (16/197) were unaware of the guideline or “aware of the guideline but have not read it”. A high proportion (76.4%; 149/195) of respondents reported regular use of the SNC-16 guideline in their respective clinical settings, and almost all (95.4%; 188/197) believed that guideline use in general optimized healthcare delivery and outcomes (Table  1 ).

Determinants of guideline use

It was common among respondents to think that colleagues (77.8%; 154/198) expected them to use the SNC-16 guideline. Fewer believed that patients (12.1%; 24/198), managers/executives in their own organization (37.9%; 75/198), a monitoring agency (Swedish National Board of Health and Welfare: 15.7%; 31/198), the government (4.0%; 8/198), and/or the professional society (23.7%; 47/198) expected them to use the guideline.

The attitude towards use of the SNC-16 guideline was generally positive as 94.9% (187/197) agreed with the content of the guideline. Approximately one of four (26.9%; 53/197) disagreed to the statement “My organization provides support (leadership, resources, assistance, etc.) needed to use this guideline”. In statement Q2.25 and Q2.27, the respondents’ perceptions of the guideline’s consistency with available evidence and how clearly the guideline describes this underlying evidence as foundation for the recommendations was explored, and the uncertainty was relatively high for both statements (“Not sure”: 37.2%; 73/196, and 47.2%; 93/197 respectively) (Table  2 ).

Enablers and barriers

Four types of enablers for guideline use emerged from the compilation of the free-text responses: ease of use and implementation, alignment with local guidelines and practice, advantages for stakeholders, and practicality and accessibility. Barriers for guideline use were manifested as: organizational challenges, medical concerns , and practical concerns (Table  3 ).

This section provided participants an opportunity to share thoughts on other determinants that could enable or challenge their use of the guideline. Noteworthy examples of "Enablers" were suggestions to extend the formal implementation among nurses, aiming to achieve a widespread adherence and acceptance of the SNC-16 guideline within all categories of healthcare professionals managing these conditions. Regarding practical concerns, ease of accessibility, e.g. laminated plastic cards in the ED, online versions, simple and unambiguous instructions, were described as enabling use of the guideline. Additionally, the importance of including disseminated guidelines, such as the SNC-16 guideline, into official local guidelines and practices was highlighted. In a broader perspective, a suggestion to gather all relevant guidelines in a bundle of nationally endorsed clinical decision-making tools was also noted.

In contrast, the absence of official organizational endorsement, both on a local and national level, emerged as a potential barrier. A specific concern raised was the fact that many Swedish physicians use the Reaction Level Scale-85 (RLS-85) [ 27 ], as opposed to the Glasgow Coma Scale (GCS) [ 28 ] recommended in the SNC-16 guideline, for assessment of level of consciousness. This discord was suggested as a barrier to adopting the SNC-16 guideline rising from inexperience in using the GCS. Challenges related to organizational practices, such as the absence of observational units and ED overcrowding, were identified as barriers affecting guideline adherence, possibly instead increasing the use of CT scanning. Within the category of medical concerns , participants expressed concern about the risk of over-investigation, encompassing both excessive observation and CT scans, and that the guideline might result in decisions that contradict the clinical judgement of experienced physicians. Concerns about the lack of clinical validation and available evidence were also raised by the respondents. The "practical concerns" category was composed around issues of complexity of guideline, time constraints, and limited availability.

In summary, the free-text responses confirmed already reported key enablers and barriers. They also provided new suggestions regarding the value of interdisciplinary collaboration among healthcare professionals and the importance of organizational structures for guideline adherence.

Learning style

Most of the respondents reported a preference for consulting colleagues (89.9%; 178/198), guidelines (75.3%; 149/198), and the internet (65.2%; 129/198) to gain knowledge to guide their clinical decisions (Fig.  2 ). Educational meetings/conferences were the most popular way to learn about guidelines (78.3%; 155/198) (Fig.  3 ). No clear preference was apparent regarding the optimal format for distribution of guideline material (Fig.  4 ).

Key sources to guide clinical decision making. 198 respondents provided answers to the multiple-choice question (4.1 in additional file 2) about the usefulness of different sources when seeking support to guide clinical decision-making. *Other = Foamed (free open access medical education) and local guidelines ( n  = 2)

Preferred ways to learn about guidelines. A total of 198 respondents provided answers to this multiple-choice question (4.2 in additional file 2). *Other = Suggested national Swedish collection of guidelines, podcasts, official medical guideline database (“Internetmedicin”), educational lunch sessions, colleagues ( n  = 6)

Preferred formats for guidelines, guideline summaries, or guideline tools ( n  = 198, multiple choice)

Associations to demographic variables

Associations between background variables and a subset of determinants were explored in Table  4 . There were significant differences between respondents that managed pediatric head injuries regularly, seldom, or rarely in their view of whether following the SNC-16 guideline would improve care delivery (91%; 79/87 versus 94%; 90/96 versus 73%; 11/15) and their view on the support provided from their organization to enable them to use the guideline (73%; 63/86 versus 52%; 50/96 versus 47%; 7/15). Those respondents that believed that guidelines (in general) optimize healthcare delivery and outcomes also had a significantly higher belief in that following the SNC-16 guideline would improve delivered care. There were no significant differences regarding gender, career stage, specialty, size of hospital, location of the respondent’s hospital in Sweden, types of patients managed, or whether the respondent had experience in guideline development for the selected determinants.

This cross-sectional survey showed that reported regular use of the passively disseminated SNC-16 guideline for pediatric mTBI was high. The respondents also held a high belief in patient benefit if applying the guideline. Improvements in the reporting of the underlying evidence and appurtenant implementation tools were requested. Barriers, such as lack of organizational support and resources, emerged both in the qualitative and quantitative data. The conveyed perception of determinants for use of the SNC-16 guideline was generally homogenous among the respondents, and independent of varying grouping variables.

The high proportion of regular guideline use (76%) reported in this study is in contrast to other reports, with only 35% adhering to guidelines in a systematic review by Mickan et al. [ 29 ] and 43% of prenatal care physicians regularly using a hepatitis C virus screening guideline in a survey by Moore et al. [ 30 ]. In a recent report on management routines at an organizational level, 55% of Swedish hospitals based their local recommendation in part or fully on the SNC-16 guideline [ 13 ]. The reason for this seemingly successful non-facilitated dissemination of the SNC-16 guideline in Sweden is unclear, although some plausible causes can be hypothesized. There is a lack of alternative, validated guidelines in Scandinavia. Also, the guidelines were published in the most common national journal and on the most commonly used web tool for doctors [ 26 , 31 ]. Additionally, a recent, non-intervention multi-center study, validated a set of pediatric mTBI guidelines in the Scandinavian healthcare system [ 32 ].

Pathman et al. [ 33 ] developed a four-step model for “leakage” of guideline evidence, from awareness to final adherence, outlining the concept of progressive loss of research evidence from guideline publication to clinical practice. The drop-off, or “leakage”, in each step of the Pathman model was estimated to be 15% in the systematic review by Mickan et al. [ 29 ]. The first step, awareness of the SNC-16 guideline, is not explicitly measured in the CGDQ. The second step is agreement with the content. If assuming that “regular use” corresponds to adoption or adherence in the Pathman framework, the leakage in this study would be between 9.25% ( agreement to adoption to adherence ) and 18.5% ( agreement to adoption ). This may raise attention to a possible, although not ascertained, discrepancy worth some effort to address in future updates of the guideline, also when considering the design of an implementation strategy. There was, for example, an uncertainty among our respondents concerning the guideline’s consistency with available evidence, which may act as a barrier for adoption and adherence. The guideline format and layout were acknowledged as easy to navigate, with clear and unambiguous wording, which may on the other hand facilitate adoption and adherence and efforts to preserve it may be beneficial [ 17 ].

In pediatric guidelines for mTBI, there has been a successive development from dichotomous prediction models based on single assessments [ 34 , 35 ], to risk group stratification at several levels (three to five) at one single time-point [ 5 , 14 ], and more recently to multiple risk groups and assessments at several time-points under observation in ED [ 36 ]. Whether the ambition to increase diagnostic accuracy via increasingly complicated flow chart structures will, at some point, limit the accessibility, final adoption and adherence to a guideline remains to be investigated, even though there have been dedicated efforts to investigate optimal implementation pathways and implementation outcome for newer mTBI guidelines both in Australia/New Zealand [ 36 , 37 ] and the US [ 38 , 39 , 40 , 41 , 42 ]. Among the Swedish respondents, a high belief in the benefit for the patients of using the SNC-16 guideline was reported in this study, which may imply that the basic flowchart structure of the clinical decision rule that is central to the guideline is feasible for the Scandinavian setting. A recent systematic review of trends in guideline implementation showed that even if more studies investigate and tailor interventions to facilitate implementation of a guideline, with most studies reporting effect, studies that did not plan specific implementation measures also achieved impact [ 20 ]. Causes for a seemingly successful dissemination of the SNC-16 guideline could therefore be numerous.

Potential barriers for implementation of the SNC-16 guideline could be identified within different types of determinants. Over one quarter of our respondents stated a lack of organizational support needed to use the guideline. Organizational barriers affect uptake of recommendations and a top-down drive of change from medical managers is likely important for adoption of a guideline, identifying team and organization leaders as a target for interventions in future implementation planning [ 39 , 43 ]. Lack of resources (e.g., observational units, CT accessibility) also seems to pose an organizational challenge in Swedish health care.

Another relevant issue are the implementation tools accompanying the SNC-16 guideline. Respondents were unsure about which tools are included in the guideline and the helpfulness of these tools. This uncertainty was also expressed as a barrier in the free-text answers. Many respondents seem to prefer electronic tools and further improvements may include development of electronic educational tools/websites and integration with electronic health record-based systems, an aspect that has been identified in other populations [ 37 , 38 , 39 , 41 ]. The need for developing more concise implementation tools, both digital and in print, was identified in an interview study investigating experience and use of the CDC pediatric mTBI guidelines in rural areas in US [ 38 ]. Recently, an evaluation of a generic model to integrate decision aids for shared decision making into electronic evidence summaries with adjacent guidelines showed promising results and may be applicable also for pediatric TBI in the future [ 44 ]. Another area amenable to improvements is the description of the underlying evidence supporting the recommendations, where only 37.6% agreed that the description was clear. This finding is in contrast to a survey by Sawka et al. [ 45 ], also using the CGDQ, which showed that 92.3% agreed that the evidence underlying the evaluated US thyroid guideline was clearly described.

More than half of the respondents sought guidance for their clinical decision-making from colleagues (90%), guidelines (75%), or the internet (65%) and preferred to learn about guidelines via educational meetings and conferences (78%). Sawka et al. [ 45 ], reported somewhat different results regarding the thyroid guideline, where the most common sources for knowledge were medical literature (88.1%), guidelines (87.2%), and colleagues (65.6%). The reported need for discussion with colleagues and learning via meetings/conferences may underscore the need for understanding stakeholders’ views of how to manage mTBI in children. Many respondents were unsure about practice in other settings, and educational meetings may fill an important knowledge gap in this respect. Daugherty et al. [ 38 ], who evaluated the implementation of the CDC pediatric mTBI guideline in a rural area in the US, identified a perceived lack of access to mTBI specialists and discussed the telemonitoring ECHO model as an example where health care providers could meet in a virtual community and discuss cases. There are reports on the application of this model in pediatric emergency care and pediatric mTBI [ 46 , 47 ]. In a recent systematic review, education of professionals was a commonly utilized intervention in guideline implementation planning [ 20 ]. Another review by Chan et al. [ 48 ] reported a positive impact through specific interventions, namely educational outreach, audit, and feedback. There was a significant association between familiarity with assessing pediatric mTBI and the perceived benefit of adherence to the recommendations. This association might be explained by senior physicians managing this condition more seldom, and when doing so relying on their clinical judgement and solid experience rather than a clinical practice guideline [ 37 ].

There are several limitations to consider when interpreting the results from this survey. The low total response rate of 43.4% (analyzable response rate 33.3%) implies a potential responder bias. The high reported use of the guideline could be an effect of sampling bias due to the modified snowball sampling method, for example if the respondents more commonly recommended colleagues with similar education, value base, or within the same organization. Nevertheless, our sampling strategy and different e-mail address collection strategies offered a good opportunity to maximize and optimize respondent relevance by drawing on snowball sampling, the ED physician community, and the ongoing guideline implementation. The background information does not, however, indicate a widespread bias among respondents as the distribution of gender, career stage, category of hospital, part of Sweden, and types of patients managed is reasonable from a Swedish healthcare perspective. Another risk worth mentioning is that of contamination, in the form of an observer effect. There has been an intense focus in Sweden on pediatric mTBI management as an effect of the ongoing guideline validation efforts. The validation study [ 32 ] is strictly observational but has inevitably set focus on the SNC-16 guidelines and the investigators behind these. However, the use of an e-mail recipient list from the 2022 study [ 13 ] is unlikely to have contaminated the responses as there was only one respondent from each of the 66 hospitals in that study. Another limitation is the cross-sectional design, addressing the physicians’ perceptions of their own actions, leaving room for deviation from the reported views in actual patient management decisions.

This cross-sectional survey on determinants for use of the Scandinavian guideline for management of mild and moderate head injury in children suggests that use of the guideline is high in our sample of ED providers in Sweden. In updated versions of the guideline, focus on improving implementation tools and descriptions of the underlying evidence may further facilitate adoption and adherence. Measures to improve organizational support for guideline use and involvement of patient representatives should also be considered.

Availability of data and materials

Pseudonymized datasets used and analyzed during the current study are available from the corresponding author on reasonable request.

Abbreviations

Scandinavian Neurotrauma Committee

Computed tomography

Emergency department

Clinical Guideline Determinants Questionnaire

Mild traumatic brain injury

Glasgow Coma Scale

Reaction Level Scale -85

Centers for Disease Control

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Acknowledgements

We would like to thank the respondents in this survey for their valuable contribution and Region Halland for ongoing support with research efforts, especially the FoUU department.

Open access funding provided by Lund University. This study was non-commercially funded by the research and development department at Halland Hospital (FoUU Halland), Sweden.

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Contributions

FW, LP, SB and JU conceived and planned the study. FW, LP and WB developed the electronic questionnaire. FW and WB compiled the respondent list. WB collected the data, with supervision by FW. FW and WB analyzed the data, summarized the results, and wrote the first draft. SK contributed with statistical supervision throughout the process. SB and JU contributed with critical review of the manuscript. All authors have read and approved the final manuscript.

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Correspondence to Fredrik Wickbom .

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The study does not include individual patient or respondent data. Ethical advisory opinion/permission was granted by the Swedish Ethical Review Authority (Dnr 2020 – 02 693) and informed consent was given by each respondent as they fulfilled the electronic questionnaire.

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Competing interests

None of the authors have any financial competing interests. SB participated in the development of the Clinician Guideline Determinants Questionnaire. JU is a member of the SNC committee, a non-profit organization independent from financial company support, who are responsible for the SNC-16 guidelines.

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Wickbom, F., Berghog, W., Bernhardsson, S. et al. Pediatric head injury guideline use in Sweden: a cross-sectional survey on determinants for successful implementation of a clinical practice guideline. BMC Health Serv Res 24 , 965 (2024). https://doi.org/10.1186/s12913-024-11423-z

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Received : 16 March 2024

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DOI : https://doi.org/10.1186/s12913-024-11423-z

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