how do you write a systematic review methodology

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How to write the methods section of a systematic review

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Covidence breaks down how to write a methods section

The methods section of your systematic review describes what you did, how you did it, and why. Readers need this information to interpret the results and conclusions of the review. Often, a lot of information needs to be distilled into just a few paragraphs. This can be a challenging task, but good preparation and the right tools will help you to set off in the right direction 🗺️🧭.

Systematic reviews are so-called because they are conducted in a way that is rigorous and replicable. So it’s important that these methods are reported in a way that is thorough, clear, and easy to navigate for the reader – whether that’s a patient, a healthcare worker, or a researcher. 

Like most things in a systematic review, the methods should be planned upfront and ideally described in detail in a project plan or protocol. Reviews of healthcare interventions follow the PRISMA guidelines for the minimum set of items to report in the methods section. But what else should be included? It’s a good idea to consider what readers will want to know about the review methods and whether the journal you’re planning to submit the work to has expectations on the reporting of methods. Finding out in advance will help you to plan what to include.

Describe what happened

While the research plan sets out what you intend to do, the methods section is a write-up of what actually happened. It’s not a simple case of rewriting the plan in the past tense – you will also need to discuss and justify deviations from the plan and describe the handling of issues that were unforeseen at the time the plan was written. For this reason, it is useful to make detailed notes before, during, and after the review is completed. Relying on memory alone risks losing valuable information and trawling through emails when the deadline is looming can be frustrating and time consuming! 

Keep it brief

The methods section should be succinct but include all the noteworthy information. This can be a difficult balance to achieve. A useful strategy is to aim for a brief description that signposts the reader to a separate section or sections of supporting information. This could include datasets, a flowchart to show what happened to the excluded studies, a collection of search strategies, and tables containing detailed information about the studies.This separation keeps the review short and simple while enabling the reader to drill down to the detail as needed. And if the methods follow a well-known or standard process, it might suffice to say so and give a reference, rather than describe the process at length. 

Follow a structure

A clear structure provides focus. Use of descriptive headings keeps the writing on track and helps the reader get to key information quickly. What should the structure of the methods section look like? As always, a lot depends on the type of review but it will certainly contain information relating to the following areas:

• Selection criteria ⭕
• Data collection and analysis 👩‍💻
• Study quality and risk of bias ⚖️

Let’s look at each of these in turn.

1. Selection criteria ⭕

The criteria for including and excluding studies are listed here. This includes detail about the types of studies, the types of participants, the types of interventions and the types of outcomes and how they were measured. 

2. Search 🕵🏾‍♀️

Comprehensive reporting of the search is important because this means it can be evaluated and replicated. The search strategies are included in the review, along with details of the databases searched. It’s also important to list any restrictions on the search (for example, language), describe how resources other than electronic databases were searched (for example,  non-indexed journals), and give the date that the searches were run. The PRISMA-S extension provides guidance on reporting literature searches. 

Systematic reviewer pro-tip:

 Copy and paste the search strategy to avoid introducing typos

3. Data collection and analysis 👩‍💻

This section describes:

• how studies were selected for inclusion in the review
• how study data were extracted from the study reports
• how study data were combined for analysis and synthesis

To describe how studies were selected for inclusion , review teams outline the screening process. Covidence uses reviewers’ decision data to automatically populate a PRISMA flow diagram for this purpose. Covidence can also calculate Cohen’s kappa to enable review teams to report the level of agreement among individual reviewers during screening.

To describe how study data were extracted from the study reports , reviewers outline the form that was used, any pilot-testing that was done, and the items that were extracted from the included studies. An important piece of information to include here is the process used to resolve conflict among the reviewers. Covidence’s data extraction tool saves reviewers’ comments and notes in the system as they work. This keeps the information in one place for easy retrieval ⚡.

To describe how study data were combined for analysis and synthesis, reviewers outline the type of synthesis (narrative or quantitative, for example), the methods for grouping data, the challenges that came up, and how these were dealt with. If the review includes a meta-analysis, it will detail how this was performed and how the treatment effects were measured.

4. Study quality and risk of bias ⚖️

Because the results of systematic reviews can be affected by many types of bias, reviewers make every effort to minimise it and to show the reader that the methods they used were appropriate. This section describes the methods used to assess study quality and an assessment of the risk of bias across a range of domains. 

Steps to assess the risk of bias in studies include looking at how study participants were assigned to treatment groups and whether patients and/or study assessors were blinded to the treatment given. Reviewers also report their assessment of the risk of bias due to missing outcome data, whether that is due to participant drop-out or non-reporting of the outcomes by the study authors.

Covidence’s default template for assessing study quality is Cochrane’s risk of bias tool but it is also possible to start from scratch and build a tool with a set of custom domains if you prefer.

Careful planning, clear writing, and a structured approach are key to a good methods section. A methodologist will be able to refer review teams to examples of good methods reporting in the literature. Covidence helps reviewers to screen references, extract data and complete risk of bias tables quickly and efficiently. Sign up for a free trial today!

Laura Mellor. Portsmouth, UK

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How to Do a Systematic Review: A Best Practice Guide for Conducting and Reporting Narrative Reviews, Meta-Analyses, and Meta-Syntheses

Affiliations.

• 1 Behavioural Science Centre, Stirling Management School, University of Stirling, Stirling FK9 4LA, United Kingdom; email: [email protected].
• 2 Department of Psychological and Behavioural Science, London School of Economics and Political Science, London WC2A 2AE, United Kingdom.
• 3 Department of Statistics, Northwestern University, Evanston, Illinois 60208, USA; email: [email protected].
• PMID: 30089228
• DOI: 10.1146/annurev-psych-010418-102803

Systematic reviews are characterized by a methodical and replicable methodology and presentation. They involve a comprehensive search to locate all relevant published and unpublished work on a subject; a systematic integration of search results; and a critique of the extent, nature, and quality of evidence in relation to a particular research question. The best reviews synthesize studies to draw broad theoretical conclusions about what a literature means, linking theory to evidence and evidence to theory. This guide describes how to plan, conduct, organize, and present a systematic review of quantitative (meta-analysis) or qualitative (narrative review, meta-synthesis) information. We outline core standards and principles and describe commonly encountered problems. Although this guide targets psychological scientists, its high level of abstraction makes it potentially relevant to any subject area or discipline. We argue that systematic reviews are a key methodology for clarifying whether and how research findings replicate and for explaining possible inconsistencies, and we call for researchers to conduct systematic reviews to help elucidate whether there is a replication crisis.

Keywords: evidence; guide; meta-analysis; meta-synthesis; narrative; systematic review; theory.

• Guidelines as Topic
• Meta-Analysis as Topic*
• Publication Bias
• Review Literature as Topic
• Systematic Reviews as Topic*

Reference management. Clean and simple.

How to write a systematic literature review [9 steps]

What is a systematic literature review?

Where are systematic literature reviews used, what types of systematic literature reviews are there, how to write a systematic literature review, 1. decide on your team, 2. formulate your question, 3. plan your research protocol, 4. search for the literature, 5. screen the literature, 6. assess the quality of the studies, 7. extract the data, 8. analyze the results, 9. interpret and present the results, registering your systematic literature review, frequently asked questions about writing a systematic literature review, related articles.

A systematic literature review is a summary, analysis, and evaluation of all the existing research on a well-formulated and specific question.

Put simply, a systematic review is a study of studies that is popular in medical and healthcare research. In this guide, we will cover:

• the definition of a systematic literature review
• the purpose of a systematic literature review
• the different types of systematic reviews
• how to write a systematic literature review

➡️ Visit our guide to the best research databases for medicine and health to find resources for your systematic review.

Systematic literature reviews can be utilized in various contexts, but they’re often relied on in clinical or healthcare settings.

Medical professionals read systematic literature reviews to stay up-to-date in their field, and granting agencies sometimes need them to make sure there’s justification for further research in an area. They can even be used as the starting point for developing clinical practice guidelines.

A classic systematic literature review can take different approaches:

• Effectiveness reviews assess the extent to which a medical intervention or therapy achieves its intended effect. They’re the most common type of systematic literature review.
• Diagnostic test accuracy reviews produce a summary of diagnostic test performance so that their accuracy can be determined before use by healthcare professionals.
• Experiential (qualitative) reviews analyze human experiences in a cultural or social context. They can be used to assess the effectiveness of an intervention from a person-centric perspective.
• Costs/economics evaluation reviews look at the cost implications of an intervention or procedure, to assess the resources needed to implement it.
• Etiology/risk reviews usually try to determine to what degree a relationship exists between an exposure and a health outcome. This can be used to better inform healthcare planning and resource allocation.
• Psychometric reviews assess the quality of health measurement tools so that the best instrument can be selected for use.
• Prevalence/incidence reviews measure both the proportion of a population who have a disease, and how often the disease occurs.
• Prognostic reviews examine the course of a disease and its potential outcomes.
• Expert opinion/policy reviews are based around expert narrative or policy. They’re often used to complement, or in the absence of, quantitative data.
• Methodology systematic reviews can be carried out to analyze any methodological issues in the design, conduct, or review of research studies.

Writing a systematic literature review can feel like an overwhelming undertaking. After all, they can often take 6 to 18 months to complete. Below we’ve prepared a step-by-step guide on how to write a systematic literature review.

• Decide on your team.
• Formulate your question.
• Plan your research protocol.
• Search for the literature.
• Screen the literature.
• Assess the quality of the studies.
• Extract the data.
• Analyze the results.
• Interpret and present the results.

When carrying out a systematic literature review, you should employ multiple reviewers in order to minimize bias and strengthen analysis. A minimum of two is a good rule of thumb, with a third to serve as a tiebreaker if needed.

You may also need to team up with a librarian to help with the search, literature screeners, a statistician to analyze the data, and the relevant subject experts.

Define your answerable question. Then ask yourself, “has someone written a systematic literature review on my question already?” If so, yours may not be needed. A librarian can help you answer this.

You should formulate a “well-built clinical question.” This is the process of generating a good search question. To do this, run through PICO:

• Patient or Population or Problem/Disease : who or what is the question about? Are there factors about them (e.g. age, race) that could be relevant to the question you’re trying to answer?
• Intervention : which main intervention or treatment are you considering for assessment?
• Comparison(s) or Control : is there an alternative intervention or treatment you’re considering? Your systematic literature review doesn’t have to contain a comparison, but you’ll want to stipulate at this stage, either way.
• Outcome(s) : what are you trying to measure or achieve? What’s the wider goal for the work you’ll be doing?

Now you need a detailed strategy for how you’re going to search for and evaluate the studies relating to your question.

The protocol for your systematic literature review should include:

• the objectives of your project
• the specific methods and processes that you’ll use
• the eligibility criteria of the individual studies
• how you plan to extract data from individual studies
• which analyses you’re going to carry out

For a full guide on how to systematically develop your protocol, take a look at the PRISMA checklist . PRISMA has been designed primarily to improve the reporting of systematic literature reviews and meta-analyses.

When writing a systematic literature review, your goal is to find all of the relevant studies relating to your question, so you need to search thoroughly .

This is where your librarian will come in handy again. They should be able to help you formulate a detailed search strategy, and point you to all of the best databases for your topic.

➡️ Read more on on how to efficiently search research databases .

The places to consider in your search are electronic scientific databases (the most popular are PubMed , MEDLINE , and Embase ), controlled clinical trial registers, non-English literature, raw data from published trials, references listed in primary sources, and unpublished sources known to experts in the field.

➡️ Take a look at our list of the top academic research databases .

Tip: Don’t miss out on “gray literature.” You’ll improve the reliability of your findings by including it.

Don’t miss out on “gray literature” sources: those sources outside of the usual academic publishing environment. They include:

• non-peer-reviewed journals
• pharmaceutical industry files
• conference proceedings
• pharmaceutical company websites
• internal reports

Gray literature sources are more likely to contain negative conclusions, so you’ll improve the reliability of your findings by including it. You should document details such as:

• The databases you search and which years they cover
• The dates you first run the searches, and when they’re updated
• Which strategies you use, including search terms
• The numbers of results obtained

➡️ Read more about gray literature .

This should be performed by your two reviewers, using the criteria documented in your research protocol. The screening is done in two phases:

• Pre-screening of all titles and abstracts, and selecting those appropriate
• Screening of the full-text articles of the selected studies

Make sure reviewers keep a log of which studies they exclude, with reasons why.

➡️ Visit our guide on what is an abstract?

Your reviewers should evaluate the methodological quality of your chosen full-text articles. Make an assessment checklist that closely aligns with your research protocol, including a consistent scoring system, calculations of the quality of each study, and sensitivity analysis.

The kinds of questions you'll come up with are:

• Were the participants really randomly allocated to their groups?
• Were the groups similar in terms of prognostic factors?
• Could the conclusions of the study have been influenced by bias?

Every step of the data extraction must be documented for transparency and replicability. Create a data extraction form and set your reviewers to work extracting data from the qualified studies.

Here’s a free detailed template for recording data extraction, from Dalhousie University. It should be adapted to your specific question.

Establish a standard measure of outcome which can be applied to each study on the basis of its effect size.

Measures of outcome for studies with:

• Binary outcomes (e.g. cured/not cured) are odds ratio and risk ratio
• Continuous outcomes (e.g. blood pressure) are means, difference in means, and standardized difference in means
• Survival or time-to-event data are hazard ratios

Design a table and populate it with your data results. Draw this out into a forest plot , which provides a simple visual representation of variation between the studies.

Then analyze the data for issues. These can include heterogeneity, which is when studies’ lines within the forest plot don’t overlap with any other studies. Again, record any excluded studies here for reference.

Consider different factors when interpreting your results. These include limitations, strength of evidence, biases, applicability, economic effects, and implications for future practice or research.

Apply appropriate grading of your evidence and consider the strength of your recommendations.

It’s best to formulate a detailed plan for how you’ll present your systematic review results. Take a look at these guidelines for interpreting results from the Cochrane Institute.

Before writing your systematic literature review, you can register it with OSF for additional guidance along the way. You could also register your completed work with PROSPERO .

Systematic literature reviews are often found in clinical or healthcare settings. Medical professionals read systematic literature reviews to stay up-to-date in their field and granting agencies sometimes need them to make sure there’s justification for further research in an area.

The first stage in carrying out a systematic literature review is to put together your team. You should employ multiple reviewers in order to minimize bias and strengthen analysis. A minimum of two is a good rule of thumb, with a third to serve as a tiebreaker if needed.

Your systematic review should include the following details:

A literature review simply provides a summary of the literature available on a topic. A systematic review, on the other hand, is more than just a summary. It also includes an analysis and evaluation of existing research. Put simply, it's a study of studies.

The final stage of conducting a systematic literature review is interpreting and presenting the results. It’s best to formulate a detailed plan for how you’ll present your systematic review results, guidelines can be found for example from the Cochrane institute .