national health and medical research council levels of evidence

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What is the “Best Evidence”?

What is “the best available evidence”? The hierarchy of evidence is a core principal of Evidence-Based Practice (EBP) and attempts to address this question. The evidence hierarchy allows you to take a top-down approach to locating the best evidence whereby you first search for a recent well-conducted systematic review and if that is not available, then move down to the next level of evidence to answer your question.

EBP hierarchies rank study types based on the rigor (strength and precision) of their research methods. Different hierarchies exist for different question types, and even experts may disagree on the exact rank of information in the evidence hierarchies. The following image represents the hierarchy of evidence provided by the National Health and Medical Research Council (NHMRC). 1

Most experts agree that the higher up the hierarchy the study design is positioned, the more rigorous the methodology and hence the more likely it is that the study design can minimize the effect of bias on the results of the study. In most evidence hierarchies current, well designed systematic reviews and meta-analyses are at the top of the pyramid, and expert opinion and anecdotal experience are at the bottom. 2

Systematic Reviews versus Primary Studies: What’s Best?

Systematic reviews and meta analyses.

Well done systematic reviews, with or without an included meta-analysis, are generally considered to provide the best evidence for all question types as they are based on the findings of multiple studies that were identified in comprehensive, systematic literature searches. However, the position of systematic reviews at the top of the evidence hierarchy is not an absolute. For example:

The process of a rigorous systematic review can take years to complete and findings can therefore be superseded by more recent evidence.
The methodological rigor and strength of findings must be appraised by the reader before being applied to patients.
A large, well conducted Randomized Controlled Trial (RCT) may provide more convincing evidence than a systematic review of smaller RCTs. 4

Primary Studies

If a current, well designed systematic review is not available, go to primary studies to answer your question. The best research designs for a primary study varies depending on the question type. The table below lists optimal study methodologies for the main types of questions.


Therapy (Treatment)	Randomized Controlled Trial (RCT)
Prevention	RCT or Prospective Study
Diagnosis	RCT or Cohort Study
Prognosis (Forecast)	Cohort Study and/or Case-Control Series
Etiology (Causation)	Cohort Study
Meaning	Qualitative Study

Note that the Clinical Queries filter available in some databases such as PubMed and CINAHL matches the question type to studies with appropriate research designs.

When searching primary literature, look first for reports of clinical trials that used the best research designs. Remember as you search, though, that the best available evidence may not come from the optimal study type. For example, if treatment effects found in well designed cohort studies are sufficiently large and consistent, those cohort studies may provide more convincing evidence than the findings of a weaker RCT.

Systematic Reviews and Narrative Reviews: What’s the Difference?

What is a systematic review.

A systematic review synthesizes the results from all available studies in a particular area, and provides a thorough analysis of the results, strengths and weaknesses of the collated studies. A systematic review has several qualities:

It addresses a focused, clearly formulated question.
It uses systematic and explicit methods:

a. to identify, select and critically appraise relevant research, and b. to collect and analyze data from the studies that are included in the review

Systematic reviews may or may not include a meta-analysis used to summaries and analyze the statistical results of included studies. This requires the studies to have the same outcome measure.

What is a Narrative Review?

Narrative reviews (often just called Reviews) are opinion with selective illustrations from the literature. They do not qualify as adequate evidence to answer clinical questions. Rather than answering a specific clinical question, they provide an overview of the research landscape on a given topic and so maybe useful for background information. Narrative reviews usually lack systematic search protocols or explicit criteria for selecting and appraising evidence and are therefore very prone to bias. 5

Filtered versus Unfiltered Information

Filtered information appraises the quality of a study and recommend its application in practice. The critical appraisal of the individual articles has already been done for you—which is a great time saver. Because the critical appraisal has been completed, filtered literature is appropriate to use for clinical decision-making at the point-of-care. In addition to saving time, filtered literature will often provide a more definitive answer than individual research reports. Examples of filtered resources include, Cochrane Database of Systematic Reviews , BMJ Clinical Evidence , and ACP Journal Club .

Unfiltered information are original research studies that have not yet been synthesized or aggregated. As such, they are the more difficult to read, interpret, and apply to practice. Examples of unfiltered resources include, CINAHL , EMBASE , Medline , and PubMe d . 3

The Cochrane Library

Cochrane Library

The Cochrane Collaboration is an international voluntary organization that prepares, maintains and promotes the accessibility of systematic reviews of the effects of healthcare.

The Cochrane Library is a database from the Cochrane Collaboration that allows simultaneous searching of six EBP databases. Cochrane Reviews are systematic reviews authored by members of the Cochrane Collaboration and available via The Cochrane Database of Systematic Reviews . They are widely recognized as the gold standard in systematic reviews due to the rigorous methodology used.

Abstracts of completed Cochrane Reviews are freely available through PubMed and Meta-Search engines such as TRIP database.

National access to the Cochrane Library is provided by the Australian Government via the National Health and Medical Research Council (NHMRC).

1. National Health and Medical Research Council. (2009). NHMRC Levels of Evidence and Grades for Recommendations for Developers of Clinical Practice Guidelines . Retrieved 2 July, 2014 from: https://www.nhmrc.gov.au/_files_nhmrc/file/guidelines/developers/nhmrc_levels_grades_evidence_120423.pdf

2. Hoffman, T., Bennett, S., & Del Mar, C. (2013). Evidence-Based Practice: Across the Health Professions (2nd ed.). Chatswood, NSW: Elsevier.

3. Kendall, S. (2008). Evidence-based resources simplified. Canadian Family Physician , 54, 241-243

4. Davidson, M., & Iles, R. (2013). Evidence-based practice in therapeutic health care. In, Liamputtong, P. (ed.). Research Methods in Health: Foundations for Evidence-Based Practice (2nd ed.). South Melbourne: Oxford University Press.

5. Cook, D., Mulrow, C., & Haynes, R. (1997). Systematic reviews: synthesis of best evidence for clinical decisions. Annals of Internal Medicine , 126, 376–80.

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Systematic Reviews

Levels of Evidence
Evidence Pyramid
Joanna Briggs Institute

The evidence pyramid is often used to illustrate the development of evidence. At the base of the pyramid is animal research and laboratory studies – this is where ideas are first developed. As you progress up the pyramid the amount of information available decreases in volume, but increases in relevance to the clinical setting.

Meta Analysis – systematic review that uses quantitative methods to synthesize and summarize the results.

Systematic Review – summary of the medical literature that uses explicit methods to perform a comprehensive literature search and critical appraisal of individual studies and that uses appropriate st atistical techniques to combine these valid studies.

Randomized Controlled Trial – Participants are randomly allocated into an experimental group or a control group and followed over time for the variables/outcomes of interest.

Cohort Study – Involves identification of two groups (cohorts) of patients, one which received the exposure of interest, and one which did not, and following these cohorts forward for the outcome of interest.

Case Control Study – study which involves identifying patients who have the outcome of interest (cases) and patients without the same outcome (controls), and looking back to see if they had the exposure of interest.

Case Series – report on a series of patients with an outcome of interest. No control group is involved.

Levels of Evidence from The Centre for Evidence-Based Medicine
The JBI Model of Evidence Based Healthcare
How to Use the Evidence: Assessment and Application of Scientific Evidence From the National Health and Medical Research Council (NHMRC) of Australia. Book must be downloaded; not available to read online.

When searching for evidence to answer clinical questions, aim to identify the highest level of available evidence. Evidence hierarchies can help you strategically identify which resources to use for finding evidence, as well as which search results are most likely to be "best".

Hierarchy of Evidence. For a text-based version, see text below image.

Image source: Evidence-Based Practice: Study Design from Duke University Medical Center Library & Archives. This work is licensed under a Creativ e Commons Attribution-ShareAlike 4.0 International License .

The hierarchy of evidence (also known as the evidence-based pyramid) is depicted as a triangular representation of the levels of evidence with the strongest evidence at the top which progresses down through evidence with decreasing strength. At the top of the pyramid are research syntheses, such as Meta-Analyses and Systematic Reviews, the strongest forms of evidence. Below research syntheses are primary research studies progressing from experimental studies, such as Randomized Controlled Trials, to observational studies, such as Cohort Studies, Case-Control Studies, Cross-Sectional Studies, Case Series, and Case Reports. Non-Human Animal Studies and Laboratory Studies occupy the lowest level of evidence at the base of the pyramid.

<< Previous: What is a Systematic Review?
Next: Locating Systematic Reviews >>
Getting Started
What is a Systematic Review?
Locating Systematic Reviews
Searching Systematically
Developing Answerable Questions
Identifying Synonyms & Related Terms
Using Truncation and Wildcards
Identifying Search Limits/Exclusion Criteria
Keyword vs. Subject Searching
Where to Search
Search Filters
Sensitivity vs. Precision
Core Databases
Other Databases
Clinical Trial Registries
Conference Presentations
Databases Indexing Grey Literature
Web Searching
Handsearching
Citation Indexes
Documenting the Search Process
Managing your Review

Research Support

Last Updated: Aug 14, 2024 11:07 AM
URL: https://guides.library.ucdavis.edu/systematic-reviews

Levels and Grades of Evidence

Chris nickson.

Nov 3, 2020

Reviewed and revised 26 August 2015

different systems of categorising the quality of evidence, and individual studies, have been developed
primarily used in evidence-based clinical guidelines

NHMRC LEVELS OF EVIDENCE

The following is the designation used by the Australian National Health and Medical Research Council (NHMRC):

Evidence obtained from a systematic review of all relevant randomised controlled trials.
Evidence obtained from at least one properly designed randomised controlled trial.
Evidence obtained from well-designed pseudo-randomised controlled trials (alternate allocation or some other method).
Evidence obtained from comparative studies with concurrent controls and allocation not randomised (cohort studies), case control studies, or interrupted time series with a control group.
Evidence obtained from comparative studies with historical control, two or more single-arm studies, or interrupted time series without a parallel control group.
Evidence obtained from case series, either post-test or pre-test and post-test.

OXFORD CENTRE FOR EVIDENCE BASED MEDICINE 2011

I – systemic review of all relevant RCTs OR an n=1 RCT
II – Randomized trial or observational study with dramatic effect
III – Non-randomized controlled cohort/follow-up study (observational)
IV – Case-series, case-control studies, or historically controlled studies
V – mechanism-based reasong (expert opinion, based on physiology, animal or laboratory studies)
A – consistent level 1 studies
B – consistent level 2 or 3 studies or extrapolations from level 1 studies
C – level 4 studies or extrapolations from level 2 or 3 studies
D – level 5 evidence or troubling inconsistent or inconclusive studies of any level

References and Links

CCC — Types of Research Studies

FOAM and web resources

Oxford Centre for Evidence-based Medicine – OCEMB Levels of Evidence System
www.GradeWorkingGroup.org

Critical Care

Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University . He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine . He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE . He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com , the RAGE podcast , the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump .

| INTENSIVE | RAGE | Resuscitology | SMACC

Levels of Evidence

Not all evidence is the same. Clearly, results from a systematic review of well conducted double-blind randomised controlled trials are much more reliable than anecdotal opinion.

NHMRC Levels of Evidence

The following is the designation used by the Australian National Health and Medical Research Council (NHMRC) [1] :

Level I Evidence obtained from a systematic review of all relevant randomised controlled trials. Level II Evidence obtained from at least one properly designed randomised controlled trial. Level III-1 Evidence obtained from well-designed pseudo-randomised controlled trials (alternate allocation or some other method). Level III-2 Evidence obtained from comparative studies with concurrent controls and allocation not randomised ( cohort studies ), case control studies , or interrupted time series with a control group. Level III-3 Evidence obtained from comparative studies with historical control, two or more single-arm studies, or interrupted time series without a parallel control group. Level IV Evidence obtained from case series , either post-test or pre-test and post-test.

Oxford Centre for Evidence Based Medicine

This is the system used by the UK National Health Service (NHS). The following has been divided into a simplified version of the “grade of recommendation” system first (the oft seen grades A to D) and then the more detailed levels of evidence [2] .

Consistent Randomised Controlled Clinical Trial, cohort study, all or none, clinical decision rule validated in different populations.
Consistent Retrospective Cohort, Exploratory Cohort, Ecological Study, Outcomes Research, case-control study; or extrapolations from level A studies.
Case-series study or extrapolations from level B studies.
Expert opinion without explicit critical appraisal, or based on physiology, bench research or first principles.

Levels of Evidence for Therapy/Prevention, Aetiology/Harm

Level 1a Systematic review with homogeneity (*) of randomised control trials Level 1b Individual randomised control trial with narrow confidence interval (studies with wide confidence interval should be tagged with a “-” at the end of their designated level). Level 1c All or none (met when all patients died before Rx became available, but some now survive on it; or when some patients died before the Rx became available but none now die on it). Level 2a Systematic review with homogeneity(*) of cohort studies Level 2b Individual cohort studies ; Low quality randomised control trials (e.g., < 80% follow up) Level 2c “Outcomes” Research; Ecological studies Level 3a Systematic review with homogeneity(*) of case-control studies Level 3b Individual case-control studies Level 4 Case series ; Poor quality cohort studies (failed to clearly define comparison groups and/or failed to measure exposures and outcomes in the same, objective way in both exposed and non-exposed individuals and/or failed to identify or appropriately control known confounders and/or failed to carry out a sufficient long and completely follow up); Poor quality case control studies (failed to clearly define comparison groups and/or failed to measure exposures and outcomes in the same, objective way in both cases and controls and/or failed to identify or appropriately control known confounders) Level 5 Expert opinion without explicit critical appraisal , or based on physiology , bench research or “first principles” . (*) A systematic review free of worrisome variations in the directions and degrees of results between individual studies. Not all systematic reviews with statistically significant heterogeneity need be worrisome, and not all worrisome heterogeneity need be statistically significant. Studies displaying worrisome heterogeneity should be tagged with a “-” at the end of their designated level.

Grade of Recommendation

A: consistent level 1 studies B: consistent level 2 or 3 studies or extrapolations from level 1 studies C: level 4 studies or extrapolations from level 2 or 3 studies D: level 5 evidence or troubling inconsistent or inconclusive studies of any level

A guide to the development, implementation and evaluation of clinical practice guidelines. NHMRC , 1999.
Levels of Evidence (March 2009). Centre for Evidence Based Medicine . Retrieved from www.cebm.net on 5 October 2010.

In this section

Evidence-Based Practice in Health

Introduction
PICO Framework and the Question Statement
Types of Clinical Question
Hierarchy of Evidence

The Evidence Hierarchy: What is the "Best Evidence"?

Systematic reviews versus primary studies: what's best, systematic reviews and narrative reviews: what's the difference, filtered versus unfiltered information, the cochrane library.

Selecting a Resource
Searching PubMed
Module 3: Appraise
Module 4: Apply
Module 5: Audit
Reference Shelf

What is "the best available evidence"? The hierarchy of evidence is a core principal of Evidence-Based Practice (EBP) and attempts to address this question. The evidence higherarchy allows you to take a top-down approach to locating the best evidence whereby you first search for a recent well-conducted systematic review and if that is not available, then move down to the next level of evidence to answer your question.

EBP hierarchies rank study types based on the rigour (strength and precision) of their research methods. Different hierarchies exist for different question types, and even experts may disagree on the exact rank of information in the evidence hierarchies. The following image represents the hierarchy of evidence provided by the National Health and Medical Research Council (NHMRC). 1

Most experts agree that the higher up the hierarchy the study design is positioned, the more rigorous the methodology and hence the more likely it is that the study design can minimise the effect of bias on the results of the study. In most evidence hierachies current, well designed systematic reviews and meta-analyses are at the top of the pyramid, and expert opinion and anecdotal experience are at the bottom. 2

Systematic Reviews and Meta Analyses

The process of a rigorous systematic review can take years to complete and findings can therefore be superseded by more recent evidence.
The methodological rigor and strength of findings must be appraised by the reader before being applied to patients.
A large, well conducted Randomised Controlled Trial (RCT) may provide more convincing evidence than a systematic review of smaller RCTs. 4

Primary Studies


Therapy (Treatment)	Randomised Contolled Trial (RCT)
Prevention	RCT or Prospective Study
Diagnosis	RCT or Cohort Study
Prognosis (Forecast)	Cohort Study and/or Case-Control Series
Etiology (Causation)	Cohort Study
Meaning	Qualitative Study

Note that the Clinical Queries filter available in some databases such as PubMed and CINAHL matches the question type to studies with appropriate research designs. When searching primary literature, look first for reports of clinical trials that used the best research designs. Remember as you search, though, that the best available evidence may not come from the optimal study type. For example, if treatment effects found in well designed cohort studies are sufficiently large and consistent, those cohort studies may provide more convincing evidence than the findings of a weaker RCT.

What is a Systematic Review?

A systematic review synthesises the results from all available studies in a particular area, and provides a thorough analysis of the results, strengths and weaknesses of the collated studies. A systematic review has several qualities:

It addresses a focused, clearly formulated question.
It uses systematic and explicit methods:

a. to identify, select and critically appraise relevant research, and b. to collect and analyse data from the studies that are included in the review

Systematic reviews may or may not include a meta-analysis used to summarise and analyse the statistical results of included studies. This requires the studies to have the same outcome measure.

What is a Narrative Review?

The Cochrane Collaboration is an international voluntary organization that prepares, maintains and promotes the accessibility of systematic reviews of the effects of healthcare.

The Cochrane Library is a database from the Cochrane Collaboration that allows simultaneous searching of six EBP databases. Cochrane Reviews are systematic reviews authored by members of the Cochrane Collaboration and available via The Cochrane Database of Systematic Reviews . They are widely recognised as the gold standard in systematic reviews due to the rigorous methodology used.

Abstracts of completed Cochrane Reviews are freely available through PubMed and Meta-Search engines such as TRIP database.

National access to the Cochrane Library is provided by the Australian Government via the National Health and Medical Research Council (NHMRC).

1. National Health and Medical Research Council. (2009). [Hierarchy of Evidence] . Retrieved 2 July, 2014 from: https://www.nhmrc.gov.au/

2. Hoffman, T., Bennett, S., & Del Mar, C. (2013). Evidence-Based Practice: Across the Health Professions (2nd ed.). Chatswood, NSW: Elsevier.

3. Kendall, S. (2008). Evidence-based resources simplified. Canadian Family Physician , 54, 241-243

5. Cook, D., Mulrow, C., & Haynes, R. (1997). Systematic reviews: synthesis of best evidence for clinical decisions. Annals of Internal Medicine , 126, 376–80.

<< Previous: Types of Clinical Question
Next: Module 2: Acquire >>
Last Updated: Jul 24, 2023 4:08 PM
URL: https://canberra.libguides.com/evidence

Levels of Evidence

Levels of evidence (or hierarchy of evidence) is a system used to rank medical studies based on the quality and reliability of their design. Levels of evidence are commonly depicted in a pyramid model that illustrates both the quality and quantity of available evidence. The higher the position on the pyramid, the stronger the evidence. 1 Each level draws on data and research previously developed in lower tiers.

Levels of evidence pyramids are often divided into two or three sections. The top section comprises filtered (secondary) evidence, including systematic reviews, meta-analyses, and critical appraisals. The section below includes unfiltered (primary) evidence, including randomized controlled trials, cohort studies, and case reports. 1 Some models include an additional bottom segment for background information and expert opinion. 2

Definitions

Systematic Review and Meta-Analysis

A systematic review synthesizes the results from all available studies of a particular health topic, answering a specific research question by collecting and evaluating all research evidence that fits the review’s selection criteria. 3 The most well-known collection of systematic reviews is the Cochrane Database of Systematic Reviews .

Systematic reviews can include meta-analyses in which statistical methods are applied to evaluate and synthesize quantitative results from multiple studies.

A randomized controlled trial (RCT) is a prospective study that measures the efficacy of an intervention or treatment. Subjects are randomly assigned to either an experimental or control group; the control group receives a placebo or sham intervention, while the experimental group receives the intervention being studied. Randomizing subjects is effective at removing bias, thus increasing the validity of the research. RCTs are frequently blinded so that neither the subjects (single blind), nor clinicians (double blind), nor the researchers (triple blind) know in which group the subjects are placed. 4

A cohort study is a type of observational study, meaning no intervention is taken among the subjects. It is also a type of longitudinal study in which research subjects are followed over a period of time. 5 A cohort study can be either prospective, which collects new data over time, or retrospective, which uses previously acquired data or medical records. This type of study examines a group of people who share a common trait or exposure and are assessed based on whether they develop an outcome of interest. An example of a prospective cohort study is a study that observes whether the subjects smoke and then many years later assesses the incidence of lung cancer in both smokers and non-smokers.

A case-control study is another type of observational study. It is also a type of retrospective study, which looks backwards in time to assess information. A case-control study compares people who have the specified condition or outcome being studied (known as the “cases”) with people who do not have the condition or outcome (known as the “controls”). 6 An example of a case-control study is a study that assesses the lifetime smoking exposure of patients with and without lung cancer.

A case report is a detailed report of the diagnosis, treatment, response to treatment, and follow-up after treatment of an individual patient. A case series is a group of case reports involving patients who were given similar treatment. A case series is observational and can be conducted either retrospectively or prospectively.

Also called a prevalence study, a cross-sectional study examines subjects at a single point in time. By definition, a cross-sectional study is only observational. 7 An example of a cross-sectional study is a survey of a population to determine the prevalence of lung cancer.

Filtered vs. Unfiltered Information

Filtered (secondary) levels of evidence is information that has been previously collected and aggregated by expert analysis and review. Filtered levels of evidence are placed above unfiltered levels of evidence on the pyramid. Examples of filtered levels are meta-analyses and systematic reviews.

Unfiltered (primary) evidence includes original research studies, including randomized controlled trials (RCTs) and case-control studies. They are often published in peer-reviewed journals. 8 However, these studies have not been subjected to additional analysis and review beyond that of the peer reviewers for each study. In most cases, unfiltered levels of evidence are difficult to apply in clinical decision-making. 9

In 1972, Archibald Cochrane, a physician from Scotland, wrote Effectiveness and Efficiency, in which he argued that decisions about medical treatment should be based on a systematic review of clinical evidence. Cochrane proposed an international collaboration of researchers to systematically review the best clinical studies in each specialty. 10

In 1979, the Canadian Task Force on the Periodic Health Examination published a ranking system for medical evidence, proposing four quality levels: 11,12

I: Evidence obtained from at least one properly randomized controlled trial
II-1: Evidence obtained from a well-designed cohort or case-control analytic studies, preferably from more than one center or research group.
II-2: Evidence obtained from comparisons between times or places with or without the intervention.
III: Opinions of respected authorities, based on clinical experience, descriptive studies, or reports of expert committees.

These levels were used to assign an alphabetic grade to the strength of individual recommendations or interventions. The U.S. Preventive Services Task Force (USPSTF) adopted a modified version of the Canadian Task Force’s categorization in 1988: 13,14

I: Evidence obtained from at least one properly designed randomized controlled trial.
II-1: Evidence obtained from well-designed controlled trials without randomization.
II-2: Evidence obtained from well-designed cohort or case-control analytic studies, preferably from more than one center or research group.
II-3: Evidence obtained from multiple time series designs with or without the intervention. Dramatic results in uncontrolled trials might also be regarded as this type of evidence.
Level III: Opinions of respected authorities, based on clinical experience, descriptive studies, or reports of expert committees.

The physician Gordon Guyatt, who in 1991 coined the term “evidence-based medicine,” proposed another approach to classifying the strength of recommendations for use in evidence-based-medicine. 15 In "Users' Guides to the Medical Literature," Guyatt expanded the Canadian Task Force’s categorization to account for new systematic procedures for combining results from different studies. 16 Referencing Guyatt’s paper, Trisha Greenhalgh summarized his revised hierarchy as follows: 17

Systematic reviews and meta-analyses
Randomized controlled trials with definitive results (confidence intervals that do not overlap the threshold of clinically significant effect)
Randomized controlled trials with non-definitive results (a point estimate that suggests a clinically significant effect but with confidence intervals overlapping the threshold for this effect)
Cohort studies
Case-control studies
Cross sectional surveys
Case reports

Evidence level definitions can vary based on the clinical question being asked (i.e. the categorization of evidence for a medical treatment may differ from evidence for determining disease prevalence). For example, The Centre for Evidence-Based Medicine and American Society of Plastic Surgeons published tables specific to therapeutic, diagnostic, and prognostic studies. 18,19

Hassan Murad, M.; Asi, N.; Alsawas, M.; Alahdab, F. “New evidence pyramid.” BMJ Evidence Based Medicine, 21(4) (2016): 125-127.
Illustration adapted from model displayed on “Evidence-Based Practice in Health.” University of Canberra Library. The model is attributed to the National Health and Medical Research Council. “NHMRC levels of evidence and grades for recommendations for guideline developers.” December 2009.
University of Canberra Library. “Evidence-Based Practice in Health.” (2020, last update.)
Hariton, E.; Locascio, J.J. “Randomised controlled trials—The gold standard for effectiveness research.” BJOG: An International Journal of Obstetrics and Gynaecology, 125(13) (2018): 1716.
Barrett, D.; Noble, H. “What are cohort studies?” Evidence Based Nursing, BMJ, 22(4) (2019): 95-96.
Himmelfarb Health Sciences Library. “Study design 101: Case control study.” (2019).
Singh Setia, M. “Methodology Series Module 3: Cross-sectional Studies.” Indian Journal of Dermatology, 61(3) (2016): 261-264.
Northern Virginia Community College. “Evidence-based practice for health professionals.” (2021, last update).
Kendall, S. “Evidence-based resources simplified.” Canadian Family Physician, 54(2) (2008): 241-243.
Stavrou, A.; Challoumas, D.; Dimitrakakis, G. “Archibald Cochrane (1909–1988): the father of evidence-based medicine.” Interactive Cardiovascular and Thoracic Surgery, 18(1) (2014): 121-124.
Spitzer, W. et al. The periodic health examination. Canadian Task Force on the Periodic Health Examination. (1979). Canadian Medical Association journal, 121(9), 1193–1254.
Burns, P. B. ; Rohrich, R. J.; Chung, K. C. “The Levels of Evidence and their Role in Evidence-Based Medicine.” Plastic and Reconstructive Surgery, 128(1) (2010): 305-310.
U.S. Preventive Services Task Force. (2018, current as of). “Grade definitions.”
U.S. Preventive Services Task Force. Guide to Clinical Preventive Services: Report of the U.S. Preventive Services Task Force. DIANE Publishing, 1989. ISBN 1568062974.
Guyatt, G. H.; Sackett, D. L.; Sinclair, J. C.; Hayward, R.; Cook, D. J.; Cook, R. J. "Users’ guides to the medical literature IX. A method for grading health care recommendations." JAMA, 274 (22) (1995): 1800-1804.
Zimerman, A. L. “Evidence-Based Medicine: A Short History of a Modern Medical Movement.” AMA Journal of Ethics, 15(1) (2013): 71-76.
Greenhalgh T. How to read a paper. Getting your bearings (deciding what the paper is about). BMJ. 1997;315(7102):243-246. doi:10.1136/bmj.315.7102.243
Sullivan D, Chung KC, Eaves FF 3rd, Rohrich RJ. The level of evidence pyramid: indicating levels of evidence in Plastic and Reconstructive Surgery articles. Plast Reconstr Surg. 2011 Jul;128(1):311-314. doi:10.1097/PRS.0b013e3182195826. PMID: 21701349.
Oxford Centre for Evidence-Based Medicine: Levels of Evidence. March 2009. CEBM.

Contributors

Moira Tannenbaum, MSN; Stacy Sebastian, MD

Published: August 17, 2021

The Pathway
Best practice statements
About the best practice statements

NHMRC Levels of Evidence

Abbreviations and Definitions

For each statement, the primary reference has been graded according the NHMRC Levels of Evidence.

NHMRC levels of evidence were chosen as the NHMRC is the major funding body of the CCRE in Aphasia Rehabilitation and the levels align with the Australian Clinical Guidelines for Stroke Management (NSF, 2010).

Table 1: NHMRC Evidence Hierarchy: designations of ‘levels of evidence’ according to type of research question

I	A systematic review of level II studies	A systematic review of level II studies	A systematic review of level II studies	A systematic review of level II studies	A systematic review of level II studies
II	A randomised controlled trial	A study of test accuracy with: an independent, blinded comparison with a valid reference standard, among consecutive persons with a defined clinical presentation	A prospective cohort study	A prospective cohort study	A randomised controlled trial
III-1	A pseudorandomised controlled trial (i.e. alternate allocation or some other method)	A study of test accuracy with: an independent, blinded comparison with a valid reference standard, among non-consecutive persons with a defined clinical presentation	All or none	All or none	A pseudorandomised controlled trial (i.e. alternate allocation or
III-2	A comparative study with concurrent controls:	A comparison with reference standard that does not meet the criteria required for Level II and III-1 evidence	Analysis of prognostic factors amongst persons in a single arm of a randomised controlled trial	A retrospective cohort study	A comparative study with concurrent controls:
III-3	A comparative study without concurrent controls:	Diagnostic case-control study	A retrospective cohort study	A case-control study	A comparative study without concurrent controls:
IV	Case series with either post-test or pre-test/post-test outcomes	Study of diagnostic yield (no reference standard)	Case series, or cohort study of persons at different stages of disease	A cross-sectional study or case series	Case series

Explanatory notes

Definitions of these study designs are provided on pages 7-8 How to use the evidence: assessment and application of scientific evidence (NHMRC 2000b).
The dimensions of evidence apply only to studies of diagnostic accuracy. To assess the effectiveness of a diagnostic test there also needs to be a consideration of the impact of the test on patient management and health outcomes (Medical Services Advisory Committee 2005, Sackett and Haynes 2002).
If it is possible and/or ethical to determine a causal relationship using experimental evidence, then the ‘Intervention’ hierarchy of evidence should be utilised. If it is only possible and/or ethical to determine a causal relationship using observational evidence (ie. cannot allocate groups to a potential harmful exposure, such as nuclear radiation), then the ‘Aetiology’ hierarchy of evidence should be utilised.
A systematic review will only be assigned a level of evidence as high as the studies it contains, excepting where those studies are of level II evidence. Systematic reviews of level II evidence provide more data than the individual studies and any meta-analyses will increase the precision of the overall results, reducing the likelihood that the results are affected by chance. Systematic reviews of lower level evidence present results of likely poor internal validity and thus are rated on the likelihood that the results have been affected by bias, rather than whether the systematic review itself is of good quality. Systematic review quality should be assessed separately. A systematic review should consist of at least two studies. In systematic reviews that include different study designs, the overall level of evidence should relate to each individual outcome/result, as different studies (and study designs) might contribute to each different outcome.
The validity of the reference standard should be determined in the context of the disease under review. Criteria for determining the validity of the reference standard should be pre-specified. This can include the choice of the reference standard(s) and its timing in relation to the index test. The validity of the reference standard can be determined through quality appraisal of the study (Whiting et al 2003).
Well-designed population based case-control studies (eg. population based screening studies where test accuracy is assessed on all cases, with a random sample of controls) do capture a population with a representative spectrum of disease and thus fulfil the requirements for a valid assembly of patients. However, in some cases the population assembled is not representative of the use of the test in practice. In diagnostic case-control studies a selected sample of patients already known to have the disease are compared with a separate group of normal/healthy people known to be free of the disease. In this situation patients with borderline or mild expressions of the disease, and conditions mimicking the disease are excluded, which can lead to exaggeration of both sensitivity and specificity. This is called spectrum bias or spectrum effect because the spectrum of study participants will not be representative of patients seen in practice (Mulherin and Miller 2002).
At study inception the cohort is either non-diseased or all at the same stage of the disease. A randomised controlled trial with persons either non-diseased or at the same stage of the disease in both arms of the trial would also meet the criterion for this level of evidence.
All or none of the people with the risk factor(s) experience the outcome; and the data arises from an unselected or representative case series which provides an unbiased representation of the prognostic effect. For example, no smallpox develops in the absence of the specific virus; and clear proof of the causal link has come from the disappearance of small pox after large-scale vaccination.
This also includes controlled before-and-after (pre-test/post-test) studies, as well as adjusted indirect comparisons (ie. utilise A vs B and B vs C, to determine A vs C with statistical adjustment for B).
Comparing single arm studies ie. case series from two studies. This would also include unadjusted indirect comparisons (ie. utilise A vs B and B vs C, to determine A vs C but where there is no statistical adjustment for B).
Studies of diagnostic yield provide the yield of diagnosed patients, as determined by an index test, without confirmation of the accuracy of this diagnosis by a reference standard. These may be the only alternative when there is no reliable reference standard.

Note A: Assessment of comparative harms/safety should occur according to the hierarchy presented for each of the research questions, with the proviso that this assessment occurs within the context of the topic being assessed. Some harms are rare and cannot feasibly be captured within randomised controlled trials; physical harms and psychological harms may need to be addressed by different study designs; harms from diagnostic testing include the likelihood of false positive and false negative results; harms from screening include the likelihood of false alarm and false reassurance results.

Source: Hierarchies adapted and modified from: NHMRC 1999; Bandolier 1999; Lijmer et al. 1999; Phillips et al. 2001.

National Health and Medical Research Council. Additional levels of evidence and grades for recommendations for developers of guidelines 2008-2010

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Extending an evidence hierarchy to include topics other than treatment: revising the Australian 'levels of evidence'

Affiliation.

1 Adelaide Health Technology Assessment (AHTA), Discipline of Public Health, University of Adelaide, South Australia, Australia. [email protected]
PMID: 19519887
PMCID: PMC2700132
DOI: 10.1186/1471-2288-9-34

Background: In 1999 a four-level hierarchy of evidence was promoted by the National Health and Medical Research Council in Australia. The primary purpose of this hierarchy was to assist with clinical practice guideline development, although it was co-opted for use in systematic literature reviews and health technology assessments. In this hierarchy interventional study designs were ranked according to the likelihood that bias had been eliminated and thus it was not ideal to assess studies that addressed other types of clinical questions. This paper reports on the revision and extension of this evidence hierarchy to enable broader use within existing evidence assessment systems.

Methods: A working party identified and assessed empirical evidence, and used a commissioned review of existing evidence assessment schema, to support decision-making regarding revision of the hierarchy. The aim was to retain the existing evidence levels I-IV but increase their relevance for assessing the quality of individual diagnostic accuracy, prognostic, aetiologic and screening studies. Comprehensive public consultation was undertaken and the revised hierarchy was piloted by individual health technology assessment agencies and clinical practice guideline developers. After two and a half years, the hierarchy was again revised and commenced a further 18 month pilot period.

Results: A suitable framework was identified upon which to model the revision. Consistency was maintained in the hierarchy of "levels of evidence" across all types of clinical questions; empirical evidence was used to support the relationship between study design and ranking in the hierarchy wherever possible; and systematic reviews of lower level studies were themselves ascribed a ranking. The impact of ethics on the hierarchy of study designs was acknowledged in the framework, along with a consideration of how harms should be assessed.

Conclusion: The revised evidence hierarchy is now widely used and provides a common standard against which to initially judge the likelihood of bias in individual studies evaluating interventional, diagnostic accuracy, prognostic, aetiologic or screening topics. Detailed quality appraisal of these individual studies, as well as grading of the body of evidence to answer each clinical, research or policy question, can then be undertaken as required.

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Yoga: Effectiveness and Safety

.header_greentext{color:green!important;font-size:24px!important;font-weight:500!important;}.header_bluetext{color:blue!important;font-size:18px!important;font-weight:500!important;}.header_redtext{color:red!important;font-size:28px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;font-size:28px!important;font-weight:500!important;}.header_purpletext{color:purple!important;font-size:31px!important;font-weight:500!important;}.header_yellowtext{color:yellow!important;font-size:20px!important;font-weight:500!important;}.header_blacktext{color:black!important;font-size:22px!important;font-weight:500!important;}.header_whitetext{color:white!important;font-size:22px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;}.Green_Header{color:green!important;font-size:24px!important;font-weight:500!important;}.Blue_Header{color:blue!important;font-size:18px!important;font-weight:500!important;}.Red_Header{color:red!important;font-size:28px!important;font-weight:500!important;}.Purple_Header{color:purple!important;font-size:31px!important;font-weight:500!important;}.Yellow_Header{color:yellow!important;font-size:20px!important;font-weight:500!important;}.Black_Header{color:black!important;font-size:22px!important;font-weight:500!important;}.White_Header{color:white!important;font-size:22px!important;font-weight:500!important;} What is yoga and how does it work?

Yoga is an ancient and complex practice, rooted in Indian philosophy. It began as a spiritual practice but has become popular as a way of promoting physical and mental well-being.

Although classical yoga also includes other elements, yoga as practiced in the United States typically emphasizes physical postures (asanas), breathing techniques (pranayama), and meditation (dyana).

There are many different yoga styles, ranging from gentle practices to physically demanding ones. Differences in the types of yoga used in research studies may affect study results. This makes it challenging to evaluate research on the health effects of yoga.

Yoga and two practices of Chinese origin— tai chi and qigong —are sometimes called “meditative movement” practices. All three practices include both meditative elements and physical ones.

.header_greentext{color:green!important;font-size:24px!important;font-weight:500!important;}.header_bluetext{color:blue!important;font-size:18px!important;font-weight:500!important;}.header_redtext{color:red!important;font-size:28px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;font-size:28px!important;font-weight:500!important;}.header_purpletext{color:purple!important;font-size:31px!important;font-weight:500!important;}.header_yellowtext{color:yellow!important;font-size:20px!important;font-weight:500!important;}.header_blacktext{color:black!important;font-size:22px!important;font-weight:500!important;}.header_whitetext{color:white!important;font-size:22px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;}.Green_Header{color:green!important;font-size:24px!important;font-weight:500!important;}.Blue_Header{color:blue!important;font-size:18px!important;font-weight:500!important;}.Red_Header{color:red!important;font-size:28px!important;font-weight:500!important;}.Purple_Header{color:purple!important;font-size:31px!important;font-weight:500!important;}.Yellow_Header{color:yellow!important;font-size:20px!important;font-weight:500!important;}.Black_Header{color:black!important;font-size:22px!important;font-weight:500!important;}.White_Header{color:white!important;font-size:22px!important;font-weight:500!important;} What are the health benefits of yoga?

Research suggests that yoga may:

Help improve general wellness by relieving stress, supporting good health habits, and improving mental/emotional health, sleep, and balance.
Relieve neck pain, migraine or tension-type headaches, and pain associated with knee osteoarthritis. It may also have a small benefit for low-back pain.
Help people with overweight or obesity lose weight.
Help people quit smoking.
Help people manage anxiety symptoms or depression.
Relieve menopause symptoms.
Be a helpful addition to treatment programs for substance use disorders.
Help people with chronic diseases manage their symptoms and improve their quality of life.

.header_greentext{color:green!important;font-size:24px!important;font-weight:500!important;}.header_bluetext{color:blue!important;font-size:18px!important;font-weight:500!important;}.header_redtext{color:red!important;font-size:28px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;font-size:28px!important;font-weight:500!important;}.header_purpletext{color:purple!important;font-size:31px!important;font-weight:500!important;}.header_yellowtext{color:yellow!important;font-size:20px!important;font-weight:500!important;}.header_blacktext{color:black!important;font-size:22px!important;font-weight:500!important;}.header_whitetext{color:white!important;font-size:22px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;}.Green_Header{color:green!important;font-size:24px!important;font-weight:500!important;}.Blue_Header{color:blue!important;font-size:18px!important;font-weight:500!important;}.Red_Header{color:red!important;font-size:28px!important;font-weight:500!important;}.Purple_Header{color:purple!important;font-size:31px!important;font-weight:500!important;}.Yellow_Header{color:yellow!important;font-size:20px!important;font-weight:500!important;}.Black_Header{color:black!important;font-size:22px!important;font-weight:500!important;}.White_Header{color:white!important;font-size:22px!important;font-weight:500!important;} What does research show about yoga for wellness?

Studies have suggested possible benefits of yoga for several aspects of wellness, including stress management, mental/emotional health, promoting healthy eating/activity habits, sleep, and balance.

.header_greentext{color:green!important;font-size:24px!important;font-weight:500!important;}.header_bluetext{color:blue!important;font-size:18px!important;font-weight:500!important;}.header_redtext{color:red!important;font-size:28px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;font-size:28px!important;font-weight:500!important;}.header_purpletext{color:purple!important;font-size:31px!important;font-weight:500!important;}.header_yellowtext{color:yellow!important;font-size:20px!important;font-weight:500!important;}.header_blacktext{color:black!important;font-size:22px!important;font-weight:500!important;}.header_whitetext{color:white!important;font-size:22px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;}.Green_Header{color:green!important;font-size:24px!important;font-weight:500!important;}.Blue_Header{color:blue!important;font-size:18px!important;font-weight:500!important;}.Red_Header{color:red!important;font-size:28px!important;font-weight:500!important;}.Purple_Header{color:purple!important;font-size:31px!important;font-weight:500!important;}.Yellow_Header{color:yellow!important;font-size:20px!important;font-weight:500!important;}.Black_Header{color:black!important;font-size:22px!important;font-weight:500!important;}.White_Header{color:white!important;font-size:22px!important;font-weight:500!important;} More

A 2020 review of 12 recent studies (672 total participants) of a variety of types of yoga for stress management in healthy adults found beneficial effects of yoga on measures of perceived stress in all the studies.
Of 17 older studies (1,070 total participants) of yoga for stress management included in a 2014 review, 12 showed improvements in physical or psychological measures related to stress.
Mental/emotional health. In a 2018 review of 14 studies (involving 1,084 total participants) that assessed the effects of yoga on positive aspects of mental health, most found evidence of benefits, such as improvements in resilience or general mental well-being.
In a 2021 study in which 60 women with obesity were randomly assigned to 12 yoga sessions or a waiting list, the beneficial effect of yoga on body mass index (BMI, an estimate of body fat based on height and weight) was found to depend on changes in physical activity and daily fruit and vegetable intake.
A 2018 survey of young adults (involving 1,820 participants) showed that practicing yoga regularly was associated with better eating and physical activity habits. In interviews, survey respondents said they thought yoga encouraged greater mindfulness and motivated them to participate in other forms of activity and to eat healthier. In addition, they saw the yoga community as a social circle that encourages connection, where healthy eating is commonplace.
In questionnaires and interviews, participants in a 2022 British study of a yoga intervention for people who were at risk for certain health conditions said that they had made changes in their lifestyles in response to the yoga program. They reported reducing consumption of unhealthy foods, increasing fruit and vegetable intake, and increasing their overall levels of physical activity.
Sleep. Yoga has been shown to be helpful for sleep in multiple studies of cancer patients, women with sleep problems, and older adults. Individual studies of population groups including health care workers, people with arthritis, and women with menopause symptoms have also reported improved sleep from yoga.
Balance. In a 2014 review, 11 of 15 studies (688 total participants) that looked at the effect of yoga on balance in healthy people showed improvements in at least one outcome related to balance. Several newer studies have provided additional evidence supporting a beneficial effect of yoga on balance in community-dwelling older adults.

.header_greentext{color:green!important;font-size:24px!important;font-weight:500!important;}.header_bluetext{color:blue!important;font-size:18px!important;font-weight:500!important;}.header_redtext{color:red!important;font-size:28px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;font-size:28px!important;font-weight:500!important;}.header_purpletext{color:purple!important;font-size:31px!important;font-weight:500!important;}.header_yellowtext{color:yellow!important;font-size:20px!important;font-weight:500!important;}.header_blacktext{color:black!important;font-size:22px!important;font-weight:500!important;}.header_whitetext{color:white!important;font-size:22px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;}.Green_Header{color:green!important;font-size:24px!important;font-weight:500!important;}.Blue_Header{color:blue!important;font-size:18px!important;font-weight:500!important;}.Red_Header{color:red!important;font-size:28px!important;font-weight:500!important;}.Purple_Header{color:purple!important;font-size:31px!important;font-weight:500!important;}.Yellow_Header{color:yellow!important;font-size:20px!important;font-weight:500!important;}.Black_Header{color:black!important;font-size:22px!important;font-weight:500!important;}.White_Header{color:white!important;font-size:22px!important;font-weight:500!important;} Can yoga help with pain management?

Research has been done on yoga for several conditions that involve pain, including low-back pain, neck pain, headaches, and knee osteoarthritis. For low-back pain, a large amount of research has been done, and the evidence suggests a slight benefit. For the other conditions, the evidence looks promising, but the amount of research is relatively small.

A 2022 review of 21 studies (2,223 total participants) of yoga interventions for low-back pain found that yoga is slightly better than no exercise, but the small difference may not be important to patients. There was evidence that participating in yoga was associated with slight improvements in physical function (ability to be active) and mental quality of life (emotional problems) in people with low-back pain. It was unclear whether there was any difference between the effects of yoga and those of other types of exercise.
A 2020 report by the Agency for Healthcare Research and Quality evaluated 10 studies of yoga for low-back pain (involving 1,520 total participants) and found that yoga improved pain and function in both the short term (1 to 6 months) and intermediate term (6 to 12 months). The effects of yoga were similar to those of exercise and massage.
A clinical practice guideline issued by the American College of Physicians in 2017 recommends using nondrug methods for the initial treatment of chronic low-back pain. Yoga is one of several suggested nondrug approaches.
Neck pain. A 2019 review of 10 studies (686 total participants) found that practicing yoga reduced the intensity of neck pain, decreased disability related to neck pain, and improved range of motion in the neck.
A 2020 review of 6 studies (240 participants) of yoga for chronic or episodic headaches (tension headaches or migraines) found evidence of reductions in headache frequency, headache duration, and pain intensity, with effects seen mostly in people with tension headaches. Because of the small numbers of studies and participants, as well as limitations in the quality of the studies, these results should be considered preliminary.
A 2022 review of 6 studies (445 participants) of yoga for migraine suggested that yoga was associated with decreases in pain intensity, headache frequency, and headache duration, and reduced the impact of migraine on daily life. However, most of the studies included small numbers of people, and the types of yoga therapy varied among studies, so the results are not conclusive. Also, most of the studies were done in Asia, and their findings might not apply to other populations.
A 2019 review of 9 studies (640 total participants) showed that yoga may be helpful for improving pain, function, and stiffness in people with osteoarthritis of the knee. However, the number of studies was small, and the research was not of high quality.
A 2019 guideline from the American College of Rheumatology and the Arthritis Foundation conditionally recommends yoga for people with knee osteoarthritis based on similarities to tai chi, which has been better studied and is strongly recommended by the same guideline.

.header_greentext{color:green!important;font-size:24px!important;font-weight:500!important;}.header_bluetext{color:blue!important;font-size:18px!important;font-weight:500!important;}.header_redtext{color:red!important;font-size:28px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;font-size:28px!important;font-weight:500!important;}.header_purpletext{color:purple!important;font-size:31px!important;font-weight:500!important;}.header_yellowtext{color:yellow!important;font-size:20px!important;font-weight:500!important;}.header_blacktext{color:black!important;font-size:22px!important;font-weight:500!important;}.header_whitetext{color:white!important;font-size:22px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;}.Green_Header{color:green!important;font-size:24px!important;font-weight:500!important;}.Blue_Header{color:blue!important;font-size:18px!important;font-weight:500!important;}.Red_Header{color:red!important;font-size:28px!important;font-weight:500!important;}.Purple_Header{color:purple!important;font-size:31px!important;font-weight:500!important;}.Yellow_Header{color:yellow!important;font-size:20px!important;font-weight:500!important;}.Black_Header{color:black!important;font-size:22px!important;font-weight:500!important;}.White_Header{color:white!important;font-size:22px!important;font-weight:500!important;} Is practicing yoga a good way to lose weight?

There’s evidence that yoga may help people lose weight.

A 2022 review of 22 studies (1,178 participants) of yoga interventions for people with overweight or obesity showed reductions in body weight, BMI, body fat, and waist size.
Longer and more frequent yoga sessions (at least 75 to 90 minutes, at least 3 times per week).
A longer duration of the overall program (3 months or more).
A yoga-based dietary component.
A residential component (such as a full weekend to start the program).
A larger number of elements of yoga.
Home practice.

.header_greentext{color:green!important;font-size:24px!important;font-weight:500!important;}.header_bluetext{color:blue!important;font-size:18px!important;font-weight:500!important;}.header_redtext{color:red!important;font-size:28px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;font-size:28px!important;font-weight:500!important;}.header_purpletext{color:purple!important;font-size:31px!important;font-weight:500!important;}.header_yellowtext{color:yellow!important;font-size:20px!important;font-weight:500!important;}.header_blacktext{color:black!important;font-size:22px!important;font-weight:500!important;}.header_whitetext{color:white!important;font-size:22px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;}.Green_Header{color:green!important;font-size:24px!important;font-weight:500!important;}.Blue_Header{color:blue!important;font-size:18px!important;font-weight:500!important;}.Red_Header{color:red!important;font-size:28px!important;font-weight:500!important;}.Purple_Header{color:purple!important;font-size:31px!important;font-weight:500!important;}.Yellow_Header{color:yellow!important;font-size:20px!important;font-weight:500!important;}.Black_Header{color:black!important;font-size:22px!important;font-weight:500!important;}.White_Header{color:white!important;font-size:22px!important;font-weight:500!important;} Can yoga help you quit smoking?

There’s evidence that yoga may help people stop smoking.

A 2019 NCCIH-funded study with 227 participants compared yoga classes with general wellness classes as additions to a conventional once-weekly counseling program. The people in the yoga group were 37 percent more likely to have quit smoking by the end of the 8-week program. However, 6 months after treatment, there was no difference between the groups in the proportion of people who were still not smoking.
A study published in 2020 showed a reduction in cigarette cravings after a single yoga session, as compared with a wellness education session. The study participants were people who were trying to cut back or stop smoking.

.header_greentext{color:green!important;font-size:24px!important;font-weight:500!important;}.header_bluetext{color:blue!important;font-size:18px!important;font-weight:500!important;}.header_redtext{color:red!important;font-size:28px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;font-size:28px!important;font-weight:500!important;}.header_purpletext{color:purple!important;font-size:31px!important;font-weight:500!important;}.header_yellowtext{color:yellow!important;font-size:20px!important;font-weight:500!important;}.header_blacktext{color:black!important;font-size:22px!important;font-weight:500!important;}.header_whitetext{color:white!important;font-size:22px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;}.Green_Header{color:green!important;font-size:24px!important;font-weight:500!important;}.Blue_Header{color:blue!important;font-size:18px!important;font-weight:500!important;}.Red_Header{color:red!important;font-size:28px!important;font-weight:500!important;}.Purple_Header{color:purple!important;font-size:31px!important;font-weight:500!important;}.Yellow_Header{color:yellow!important;font-size:20px!important;font-weight:500!important;}.Black_Header{color:black!important;font-size:22px!important;font-weight:500!important;}.White_Header{color:white!important;font-size:22px!important;font-weight:500!important;} How does yoga affect mental health?

Yoga can be a helpful addition to treatment for depression. It may also be helpful for anxiety symptoms in a variety of populations, but there’s little evidence of a benefit for people with anxiety disorders. Yoga might have benefits for people with post-traumatic stress disorder (PTSD).

.header_greentext{color:green!important;font-size:24px!important;font-weight:500!important;}.header_bluetext{color:blue!important;font-size:18px!important;font-weight:500!important;}.header_redtext{color:red!important;font-size:28px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;font-size:28px!important;font-weight:500!important;}.header_purpletext{color:purple!important;font-size:31px!important;font-weight:500!important;}.header_yellowtext{color:yellow!important;font-size:20px!important;font-weight:500!important;}.header_blacktext{color:black!important;font-size:22px!important;font-weight:500!important;}.header_whitetext{color:white!important;font-size:22px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;}.Green_Header{color:green!important;font-size:24px!important;font-weight:500!important;}.Blue_Header{color:blue!important;font-size:18px!important;font-weight:500!important;}.Red_Header{color:red!important;font-size:28px!important;font-weight:500!important;}.Purple_Header{color:purple!important;font-size:31px!important;font-weight:500!important;}.Yellow_Header{color:yellow!important;font-size:20px!important;font-weight:500!important;}.Black_Header{color:black!important;font-size:22px!important;font-weight:500!important;}.White_Header{color:white!important;font-size:22px!important;font-weight:500!important;} Depression

In a 2017 review of 23 studies (involving 1,272 participants) of people with depressive symptoms (although not necessarily diagnosed with depression), yoga was helpful in reducing symptoms in 14 of the studies.
A 2020 review of 7 studies (260 participants) of yoga interventions for people who had been diagnosed with major depressive disorder concluded that yoga may have small additional benefits for depression symptoms when used along with other forms of treatment.

.header_greentext{color:green!important;font-size:24px!important;font-weight:500!important;}.header_bluetext{color:blue!important;font-size:18px!important;font-weight:500!important;}.header_redtext{color:red!important;font-size:28px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;font-size:28px!important;font-weight:500!important;}.header_purpletext{color:purple!important;font-size:31px!important;font-weight:500!important;}.header_yellowtext{color:yellow!important;font-size:20px!important;font-weight:500!important;}.header_blacktext{color:black!important;font-size:22px!important;font-weight:500!important;}.header_whitetext{color:white!important;font-size:22px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;}.Green_Header{color:green!important;font-size:24px!important;font-weight:500!important;}.Blue_Header{color:blue!important;font-size:18px!important;font-weight:500!important;}.Red_Header{color:red!important;font-size:28px!important;font-weight:500!important;}.Purple_Header{color:purple!important;font-size:31px!important;font-weight:500!important;}.Yellow_Header{color:yellow!important;font-size:20px!important;font-weight:500!important;}.Black_Header{color:black!important;font-size:22px!important;font-weight:500!important;}.White_Header{color:white!important;font-size:22px!important;font-weight:500!important;} Anxiety

A 2019 review of 38 studies (2,295 participants) of yoga for anxiety symptoms found that yoga had a substantial beneficial effect, with the greatest effects seen in studies performed in India. The studies included a variety of different groups of people, including healthy people such as students and military personnel, patients with various physical or mental health conditions, and caregivers.
A 2021 review looked at the evidence on yoga for people who have been diagnosed with anxiety disorders. The reviewers identified some promising results, but they were unable to reach conclusions about whether yoga is helpful because not enough rigorous studies have been done.
A 2021 study of Kundalini yoga for generalized anxiety disorder (226 participants, 155 of whom completed the study), supported by NCCIH, found that Kundalini yoga improved symptoms but was less helpful than cognitive behavioral therapy, an established first-line treatment for this condition.

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A 2018 evaluation of 7 studies (284 participants) of yoga for people with post-traumatic stress disorder (PTSD) found only low-quality evidence of a possible benefit.

.header_greentext{color:green!important;font-size:24px!important;font-weight:500!important;}.header_bluetext{color:blue!important;font-size:18px!important;font-weight:500!important;}.header_redtext{color:red!important;font-size:28px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;font-size:28px!important;font-weight:500!important;}.header_purpletext{color:purple!important;font-size:31px!important;font-weight:500!important;}.header_yellowtext{color:yellow!important;font-size:20px!important;font-weight:500!important;}.header_blacktext{color:black!important;font-size:22px!important;font-weight:500!important;}.header_whitetext{color:white!important;font-size:22px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;}.Green_Header{color:green!important;font-size:24px!important;font-weight:500!important;}.Blue_Header{color:blue!important;font-size:18px!important;font-weight:500!important;}.Red_Header{color:red!important;font-size:28px!important;font-weight:500!important;}.Purple_Header{color:purple!important;font-size:31px!important;font-weight:500!important;}.Yellow_Header{color:yellow!important;font-size:20px!important;font-weight:500!important;}.Black_Header{color:black!important;font-size:22px!important;font-weight:500!important;}.White_Header{color:white!important;font-size:22px!important;font-weight:500!important;} Can yoga help with menopause symptoms?

Yoga seems to be at least as effective as other types of exercise in relieving menopause symptoms. A 2018 evaluation of 13 studies (more than 1,300 participants) of yoga for menopause symptoms found that yoga reduced physical symptoms such as hot flashes as well as psychological symptoms such as anxiety or depression.

.header_greentext{color:green!important;font-size:24px!important;font-weight:500!important;}.header_bluetext{color:blue!important;font-size:18px!important;font-weight:500!important;}.header_redtext{color:red!important;font-size:28px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;font-size:28px!important;font-weight:500!important;}.header_purpletext{color:purple!important;font-size:31px!important;font-weight:500!important;}.header_yellowtext{color:yellow!important;font-size:20px!important;font-weight:500!important;}.header_blacktext{color:black!important;font-size:22px!important;font-weight:500!important;}.header_whitetext{color:white!important;font-size:22px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;}.Green_Header{color:green!important;font-size:24px!important;font-weight:500!important;}.Blue_Header{color:blue!important;font-size:18px!important;font-weight:500!important;}.Red_Header{color:red!important;font-size:28px!important;font-weight:500!important;}.Purple_Header{color:purple!important;font-size:31px!important;font-weight:500!important;}.Yellow_Header{color:yellow!important;font-size:20px!important;font-weight:500!important;}.Black_Header{color:black!important;font-size:22px!important;font-weight:500!important;}.White_Header{color:white!important;font-size:22px!important;font-weight:500!important;} Is yoga helpful for substance use disorders?

A small amount of research has looked at the possible benefits of incorporating yoga into treatment programs for various types of substance use disorders (opioid, alcohol, or tobacco use disorders or others). In a 2021 review of 8 studies (1,889 participants), 7 studies showed evidence of beneficial effects in terms of reduced use of the substance or reduction in symptoms such as pain, stress, or anxiety.

.header_greentext{color:green!important;font-size:24px!important;font-weight:500!important;}.header_bluetext{color:blue!important;font-size:18px!important;font-weight:500!important;}.header_redtext{color:red!important;font-size:28px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;font-size:28px!important;font-weight:500!important;}.header_purpletext{color:purple!important;font-size:31px!important;font-weight:500!important;}.header_yellowtext{color:yellow!important;font-size:20px!important;font-weight:500!important;}.header_blacktext{color:black!important;font-size:22px!important;font-weight:500!important;}.header_whitetext{color:white!important;font-size:22px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;}.Green_Header{color:green!important;font-size:24px!important;font-weight:500!important;}.Blue_Header{color:blue!important;font-size:18px!important;font-weight:500!important;}.Red_Header{color:red!important;font-size:28px!important;font-weight:500!important;}.Purple_Header{color:purple!important;font-size:31px!important;font-weight:500!important;}.Yellow_Header{color:yellow!important;font-size:20px!important;font-weight:500!important;}.Black_Header{color:black!important;font-size:22px!important;font-weight:500!important;}.White_Header{color:white!important;font-size:22px!important;font-weight:500!important;} Is yoga helpful for people with chronic diseases?

There’s promising evidence that yoga may help people with some chronic diseases manage their symptoms and improve their quality of life. Thus, yoga could be a helpful addition to treatment programs.

In a 2018 evaluation of 138 studies on the use of yoga in patients with various types of cancer (10,660 total participants), most of the studies found that yoga improved patients’ physical and psychological symptoms and quality of life.
A 2021 review looked at 26 studies of yoga for depressive symptoms (1,486 participants) and 16 studies of yoga for anxiety symptoms (977 participants) in people with cancer. Small-to-moderate beneficial effects were seen for both types of symptoms.
Many yoga studies have focused on women who have or have had breast cancer. A 2022 review examined 23 studies that looked at the effects of yoga interventions on various symptoms in women with breast cancer during active cancer treatment. The majority of the studies showed significant benefits of yoga on quality of life, fatigue, nausea/vomiting, sleep quality, anxiety, depression, stress, or wound healing, suggesting that yoga may be helpful for symptom management.
A review of 8 studies (92 participants) suggested that yoga may have benefits for sleep, anxiety, fatigue, and quality of life in children and adolescents with cancer.
Chronic obstructive pulmonary disease (COPD). A 2019 review of 11 studies (586 participants) of breathing-focused yoga interventions for people with Parkinson’s disease found beneficial effects of these interventions on exercise capacity, lung function, and quality of life.
HIV/AIDS. A 2019 review of 7 studies (396 participants) of yoga interventions for people with HIV/AIDS found that yoga was a promising intervention for stress management.
A 2016 review of 15 studies of yoga for asthma (involving 1,048 total participants, most of whom were adults) concluded that yoga probably leads to small improvements in quality of life and symptoms.
A 2020 review of 9 studies (1,230 participants) of yoga-based interventions for children or adolescents with asthma found that the use of yoga was associated with improvements in lung function, stress/anxiety, and quality of life. However, because of wide variation in both the populations who were studied and the yoga interventions that were tested, it was unclear which components of yoga and how much yoga are needed to provide benefits.
Multiple sclerosis. Two recent reviews on yoga for people with multiple sclerosis showed little evidence of benefits. One review found a significant benefit only for fatigue (comparable to the effect of other types of exercise), and the other found no benefits for any aspect of quality of life.
Parkinson’s disease. A 2022 review (14 studies, 444 participants) suggests that yoga may have benefits for mobility, balance, and quality of life for people with mild-to-moderate Parkinson’s disease. The studies that were reviewed also suggest that yoga interventions are safe and acceptable for people with this condition.

.header_greentext{color:green!important;font-size:24px!important;font-weight:500!important;}.header_bluetext{color:blue!important;font-size:18px!important;font-weight:500!important;}.header_redtext{color:red!important;font-size:28px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;font-size:28px!important;font-weight:500!important;}.header_purpletext{color:purple!important;font-size:31px!important;font-weight:500!important;}.header_yellowtext{color:yellow!important;font-size:20px!important;font-weight:500!important;}.header_blacktext{color:black!important;font-size:22px!important;font-weight:500!important;}.header_whitetext{color:white!important;font-size:22px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;}.Green_Header{color:green!important;font-size:24px!important;font-weight:500!important;}.Blue_Header{color:blue!important;font-size:18px!important;font-weight:500!important;}.Red_Header{color:red!important;font-size:28px!important;font-weight:500!important;}.Purple_Header{color:purple!important;font-size:31px!important;font-weight:500!important;}.Yellow_Header{color:yellow!important;font-size:20px!important;font-weight:500!important;}.Black_Header{color:black!important;font-size:22px!important;font-weight:500!important;}.White_Header{color:white!important;font-size:22px!important;font-weight:500!important;} What does research show about practicing yoga during pregnancy?

Physical activities such as yoga are safe and desirable for most pregnant women as long as appropriate precautions are taken. Yoga may have health benefits for pregnant women, such as decreasing stress, anxiety, and depression.

If you are pregnant, you should be evaluated by your health care provider to make sure there’s no medical reason why you shouldn’t exercise.
You may need to modify some activities, including yoga, during pregnancy. You should avoid “hot yoga” while you are pregnant because it can cause overheating. You also need to avoid activities, including yoga poses, that involve long periods of being still or lying on your back. Talk with your health care provider about how to adjust your physical activity during pregnancy.
A 2022 analysis of 29 studies of pregnancy yoga interventions (2,217 participants) found that these programs reduced anxiety, depression, perceived stress, and duration of labor and increased the likelihood of a normal vaginal birth. However, because the yoga programs varied widely and because some of the studies had weaknesses in their methods, additional rigorous research is needed to better understand the effects of yoga during pregnancy and to find out what types of yoga programs are best in terms of both effectiveness and safety.

.header_greentext{color:green!important;font-size:24px!important;font-weight:500!important;}.header_bluetext{color:blue!important;font-size:18px!important;font-weight:500!important;}.header_redtext{color:red!important;font-size:28px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;font-size:28px!important;font-weight:500!important;}.header_purpletext{color:purple!important;font-size:31px!important;font-weight:500!important;}.header_yellowtext{color:yellow!important;font-size:20px!important;font-weight:500!important;}.header_blacktext{color:black!important;font-size:22px!important;font-weight:500!important;}.header_whitetext{color:white!important;font-size:22px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;}.Green_Header{color:green!important;font-size:24px!important;font-weight:500!important;}.Blue_Header{color:blue!important;font-size:18px!important;font-weight:500!important;}.Red_Header{color:red!important;font-size:28px!important;font-weight:500!important;}.Purple_Header{color:purple!important;font-size:31px!important;font-weight:500!important;}.Yellow_Header{color:yellow!important;font-size:20px!important;font-weight:500!important;}.Black_Header{color:black!important;font-size:22px!important;font-weight:500!important;}.White_Header{color:white!important;font-size:22px!important;font-weight:500!important;} Does yoga have benefits for children?

Research suggests that yoga may have several potential benefits for children.

A 2020 review of 27 studies (1,805 total participants) of yoga interventions in children or adolescents found reductions in anxiety or depression in 70 percent of the studies, with more promising results for anxiety. Some of the studies involved children who had or were at risk for various physical or mental health disorders and others involved groups of children in schools. The quality of the studies was relatively weak, and the results cannot be considered conclusive.
A 2021 review evaluated 9 studies (289 total participants) of yoga interventions for weight loss in children or adolescents with obesity or overweight. Some of the studies evaluated yoga alone; others evaluated yoga in combination with other interventions such as changes in diet. The majority of the yoga interventions had beneficial effects on weight loss and related behavior changes. The studies were small, and some did not use the most rigorous study designs.
A 2022 review of 21 studies (2,227 participants) of school-based yoga interventions in students age 5 to 15 showed promising results suggesting that yoga may enhance mental health among children and adolescents.
Yoga interventions in educational settings have also been studied in preschool-aged children (age 3 to 5). A 2021 review of studies of yoga and mindfulness practices in this age group suggested that these practices may have benefits for social-emotional functioning, although more research is needed before definite conclusions can be reached.
A small amount of evidence suggests that school-based yoga programs may have academic and psychological benefits for neurodiverse children.

.header_greentext{color:green!important;font-size:24px!important;font-weight:500!important;}.header_bluetext{color:blue!important;font-size:18px!important;font-weight:500!important;}.header_redtext{color:red!important;font-size:28px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;font-size:28px!important;font-weight:500!important;}.header_purpletext{color:purple!important;font-size:31px!important;font-weight:500!important;}.header_yellowtext{color:yellow!important;font-size:20px!important;font-weight:500!important;}.header_blacktext{color:black!important;font-size:22px!important;font-weight:500!important;}.header_whitetext{color:white!important;font-size:22px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;}.Green_Header{color:green!important;font-size:24px!important;font-weight:500!important;}.Blue_Header{color:blue!important;font-size:18px!important;font-weight:500!important;}.Red_Header{color:red!important;font-size:28px!important;font-weight:500!important;}.Purple_Header{color:purple!important;font-size:31px!important;font-weight:500!important;}.Yellow_Header{color:yellow!important;font-size:20px!important;font-weight:500!important;}.Black_Header{color:black!important;font-size:22px!important;font-weight:500!important;}.White_Header{color:white!important;font-size:22px!important;font-weight:500!important;} What are the risks of yoga?

Yoga is generally considered a safe form of physical activity for healthy people when performed properly, under the guidance of a qualified instructor. However, as with other forms of physical activity, injuries can occur. The most common injuries are sprains and strains, and the parts of the body most commonly injured are the knee or lower leg. Serious injuries are rare. The risk of injury associated with yoga is lower than that for higher impact physical activities.

Older adults may need to be particularly cautious when practicing yoga. The rate of yoga-related injuries treated in emergency departments is higher in people age 65 and older than in younger adults.

To reduce your chances of getting hurt while doing yoga:

Practice yoga under the guidance of a qualified instructor. Learning yoga on your own without supervision has been associated with increased risks.
If you’re new to yoga, avoid extreme practices such as headstands, shoulder stands, the lotus position, and forceful breathing.
Be aware that hot yoga has special risks related to overheating and dehydration.
Pregnant women, older adults, and people with health conditions should talk with their health care providers and the yoga instructor about their individual needs. They may need to avoid or modify some yoga poses and practices. Some of the health conditions that may call for modifications in yoga include preexisting injuries, such as knee or hip injuries, lumbar spine disease, severe high blood pressure, balance issues, and glaucoma.

.header_greentext{color:green!important;font-size:24px!important;font-weight:500!important;}.header_bluetext{color:blue!important;font-size:18px!important;font-weight:500!important;}.header_redtext{color:red!important;font-size:28px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;font-size:28px!important;font-weight:500!important;}.header_purpletext{color:purple!important;font-size:31px!important;font-weight:500!important;}.header_yellowtext{color:yellow!important;font-size:20px!important;font-weight:500!important;}.header_blacktext{color:black!important;font-size:22px!important;font-weight:500!important;}.header_whitetext{color:white!important;font-size:22px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;}.Green_Header{color:green!important;font-size:24px!important;font-weight:500!important;}.Blue_Header{color:blue!important;font-size:18px!important;font-weight:500!important;}.Red_Header{color:red!important;font-size:28px!important;font-weight:500!important;}.Purple_Header{color:purple!important;font-size:31px!important;font-weight:500!important;}.Yellow_Header{color:yellow!important;font-size:20px!important;font-weight:500!important;}.Black_Header{color:black!important;font-size:22px!important;font-weight:500!important;}.White_Header{color:white!important;font-size:22px!important;font-weight:500!important;} How popular is yoga in the United States?

According to a national survey, the percentage of U.S. adults who practiced yoga increased from 5.0 percent in 2002 to 15.8 percent in 2022.

For children, there are data from 2017; in that year, 8.4 percent of U.S. children age 4 to 17 practiced yoga.

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National survey data from 2012 showed that 94 percent of adults who practiced yoga did it for wellness-related reasons, while 17.5 percent did it to treat a specific health condition. Some people reported doing both.

.header_greentext{color:green!important;font-size:24px!important;font-weight:500!important;}.header_bluetext{color:blue!important;font-size:18px!important;font-weight:500!important;}.header_redtext{color:red!important;font-size:28px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;font-size:28px!important;font-weight:500!important;}.header_purpletext{color:purple!important;font-size:31px!important;font-weight:500!important;}.header_yellowtext{color:yellow!important;font-size:20px!important;font-weight:500!important;}.header_blacktext{color:black!important;font-size:22px!important;font-weight:500!important;}.header_whitetext{color:white!important;font-size:22px!important;font-weight:500!important;}.header_darkred{color:#803d2f!important;}.Green_Header{color:green!important;font-size:24px!important;font-weight:500!important;}.Blue_Header{color:blue!important;font-size:18px!important;font-weight:500!important;}.Red_Header{color:red!important;font-size:28px!important;font-weight:500!important;}.Purple_Header{color:purple!important;font-size:31px!important;font-weight:500!important;}.Yellow_Header{color:yellow!important;font-size:20px!important;font-weight:500!important;}.Black_Header{color:black!important;font-size:22px!important;font-weight:500!important;}.White_Header{color:white!important;font-size:22px!important;font-weight:500!important;} Do different groups of people have different experiences with yoga?

Much of the research on yoga in the United States has been conducted in predominantly female, non-Hispanic White, well-educated people with relatively high incomes. Other people—particularly members of minority groups and those with lower incomes—have been underrepresented in yoga studies.

Different groups of people may have different yoga-related experiences, and the results of studies that did not examine a diverse population may not apply to everyone.

Differences related to age. In one survey, people age 40 to 54 were more likely to be motivated to practice yoga to increase muscle strength or lose weight, while those age 55 or older were more likely to be motivated by age-related chronic health issues. People age 65 and older may be more likely to need treatment for yoga-related injuries.
Differences related to gender. A study found evidence for differences between men and women in the effects of specific yoga poses on muscles. A study in veterans found preliminary evidence that women might benefit more than men from yoga interventions for chronic back pain.
Differences related to Hispanic ethnicity. U.S. national survey data show lower participation in yoga among Hispanic adults, compared to non-Hispanic White adults (8.0 percent vs. 17.1 percent of adults in 2017). A small 2021 survey of U.S. Hispanic adults with low incomes showed that cost was the most common barrier to participation in yoga. Other perceived barriers included concern about the need for physical flexibility (especially among men and those with no prior experience with yoga), thinking that they would feel like outsiders in a yoga class (among those with no prior experience), and considering yoga boring (among young adults).

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NCCIH is sponsoring a variety of yoga studies, including:

An evaluation of emotion regulation as a mechanism of action in yoga interventions for chronic low-back pain.
A study of yoga for chronic pain in people who are being treated for opioid use disorder.
A study of the effects of yoga postures and slow, deep breathing in people with hypertension (high blood pressure).

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Don’t use yoga to postpone seeing a health care provider about a medical problem.
Ask about the training and experience of the yoga instructor you’re considering.
Take charge of your health—talk with your health care providers about any complementary health approaches you use. Together, you can make shared, well-informed  decisions.

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Website: https://pubmed.ncbi.nlm.nih.gov/

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Seshadri A, Adaji A, Orth SS, et al. Exercise, yoga, and tai chi for treatment of major depressive disorder in outpatient settings: a systematic review and meta-analysis . Primary Care Companion for CNS Disorders. 2020;23(1):20r2722.
Skelly AC, Chou R, Dettori JR, et al. Noninvasive Nonpharmacological Treatment for Chronic Pain: A Systematic Review Update. Comparative Effectiveness Review no. 227. Rockville, MD: Agency for Healthcare Research and Quality; 2020. AHRQ publication no. 20-EHC009.
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Agarwal RP, Maroko-Afek A. Yoga into cancer care: a review of the evidence-based research. International Journal of Yoga. 2018;11(1):3-29.
Alphonsus KB, Su Y, D’Arcy C. The effect of exercise, yoga and physiotherapy on the quality of life in people with multiple sclerosis: systematic review and meta-analysis. Complementary Therapies in Medicine. 2019;43:188-195.
Anheyer D, Koch AK, Thoms MS, et al. Yoga in women with abdominal obesity—do lifestyle factors mediate the effect? Secondary analysis of a RCT. Complementary Therapies in Medicine. 2021;60:102741.
Bandealy SS, Sheth NC, Matuella SK, et al. Mind-body interventions for anxiety disorders: a review of the evidence base for mental health practitioners . Focus (American Psychiatric Publishing). 2021;19(2):173-183.
Bolgla LA, Amodio L, Archer K, et al. Trunk and hip muscle activation during yoga poses: do sex-differences exist? Complementary Therapies in Clinical Practice. 2018;31:256-261.
Bridges L, Sharma M. The efficacy of yoga as a form of treatment for depression. Journal of Evidence-Based Complementary and Alternative Medicine. 2017;22(4):1017-1028.
Cheshire A, Richards R, Cartwright T. ‘Joining a group was inspiring’: a qualitative study of service users’ experiences of yoga on social prescription. BMC Complementary Medicine and Therapies. 2022;22(1):67.
Cocchiara RA, Peruzzo M, Mannocci A, et al. The use of yoga to manage stress and burnout in healthcare workers: a systematic review. Journal of Clinical Medicine. 2019;8(3):284.
Cramer H, Anheyer D, Saha FJ, et al. Yoga for posttraumatic stress disorder—a systematic review and meta-analysis. BMC Psychiatry. 2018;18(1):72.
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Cramer H, Peng W, Lauche R. Yoga for menopausal symptoms—a systematic review and meta-analysis. Maturitas. 2018;109:13-25.
Cramer H, Quinker D, Schumann D, et al. Adverse effects of yoga: a national cross-sectional survey. BMC Complementary and Alternative Medicine. 2019;19(1):190.
Cramer H, Ward L, Steel A, et al. Prevalence, patterns, and predictors of yoga use: results of a U.S. nationally representative survey. American Journal of Preventive Medicine. 2016;50(2):230-235.
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Acknowledgments

NCCIH thanks Inna Belfer, M.D., Ph.D., and David Shurtleff, Ph.D., NCCIH, for their review of the 2023 update of this publication.

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Extending an evidence hierarchy to include topics other than treatment: revising the Australian 'levels of evidence'

Tracy merlin.

1 Adelaide Health Technology Assessment (AHTA), Discipline of Public Health, University of Adelaide, Adelaide, South Australia, Australia

Adele Weston

2 Health Technology Analysts, Balmain, New South Wales, Australia

Rebecca Tooher

3 Discipline of Obstetrics and Gynaecology, University of Adelaide, Adelaide, South Australia, Australia

Associated Data

In 1999 a four-level hierarchy of evidence was promoted by the National Health and Medical Research Council in Australia. The primary purpose of this hierarchy was to assist with clinical practice guideline development, although it was co-opted for use in systematic literature reviews and health technology assessments. In this hierarchy interventional study designs were ranked according to the likelihood that bias had been eliminated and thus it was not ideal to assess studies that addressed other types of clinical questions. This paper reports on the revision and extension of this evidence hierarchy to enable broader use within existing evidence assessment systems.

A working party identified and assessed empirical evidence, and used a commissioned review of existing evidence assessment schema, to support decision-making regarding revision of the hierarchy. The aim was to retain the existing evidence levels I-IV but increase their relevance for assessing the quality of individual diagnostic accuracy, prognostic, aetiologic and screening studies. Comprehensive public consultation was undertaken and the revised hierarchy was piloted by individual health technology assessment agencies and clinical practice guideline developers. After two and a half years, the hierarchy was again revised and commenced a further 18 month pilot period.

A suitable framework was identified upon which to model the revision. Consistency was maintained in the hierarchy of "levels of evidence" across all types of clinical questions; empirical evidence was used to support the relationship between study design and ranking in the hierarchy wherever possible; and systematic reviews of lower level studies were themselves ascribed a ranking. The impact of ethics on the hierarchy of study designs was acknowledged in the framework, along with a consideration of how harms should be assessed.

The revised evidence hierarchy is now widely used and provides a common standard against which to initially judge the likelihood of bias in individual studies evaluating interventional, diagnostic accuracy, prognostic, aetiologic or screening topics. Detailed quality appraisal of these individual studies, as well as grading of the body of evidence to answer each clinical, research or policy question, can then be undertaken as required.

The corner-stone of evidence-based healthcare and health technology assessment is critical appraisal of the evidence underpinning a finding. Different methods are available for assessing the quality of the evidence, including ranking the body of evidence according to a hierarchy which indicates the level of bias associated with the different study designs that have contributed to the evidence-base. In Australia, the standard evidence hierarchy in use since 1999 has been the National Health and Medical Research Council (NHMRC) Designation of Levels of Evidence [ 1 ]. This hierarchy ranks the body of evidence into four levels – from systematic reviews of randomised trials at the top of the hierarchy, to case series and case reports at the bottom of the hierarchy (Table (Table1). 1 ). Its intended purpose was to summarise the body of evidence for interventions (eg treatment effectiveness). Through widespread use in clinical practice guideline development and health technology assessment, it became increasingly clear that: i) the hierarchy was being used to address research questions that did not relate to interventions; ii) the hierarchy – which is primarily concerned with the association between bias and study design characteristics – was being relied upon for the entire evidence appraisal rather than there being a standardised appraisal of study quality as suggested [ 2 ]; and iii) that although the aim was to use the hierarchy to summarise the entire body of evidence – this was occurring rather haphazardly in practice.

Designations of levels of evidence [ 1 ]

Level of evidence	Study design
I	Evidence obtained from a systematic review of all relevant randomised controlled trials
II	Evidence obtained from at least one properly-designed randomised controlled trial
III-1	Evidence obtained from well-designed pseudorandomised controlled trials (alternate allocation or some other method)
III-2	Evidence obtained from comparative studies (including systematic reviews of such studies) with concurrent controls and allocation not randomised, cohort studies, case-control studies, or interrupted time series with a control group
III-3	Evidence obtained from comparative studies with historical control, two or more single arm studies, or interrupted time series without a parallel control group
IV	Evidence obtained from case series, either post-test or pre-test/post-test

This paper describes the first stage of developing a hierarchy to rank the quality of individual study designs to address different types of questions. The second stage of developing or adapting a simple, intuitive system to grade the entire body of evidence is discussed elsewhere [ 3 , 4 ], and will be the subject of a forthcoming publication.

The existing hierarchy

The existing NHMRC hierarchy of evidence was developed as part of a comprehensive series of handbooks which outlined the methods for evaluating evidence and developing and disseminating clinical practice guidelines [ 1 , 2 , 5 - 9 ].

These handbooks recommended that the body of evidence should be assessed along three dimensions: strength, size of effect and clinical relevance. In this schema the strength of evidence was determined by the level of evidence, the quality of the evidence and its statistical precision. It was further assumed that the results from a 'body of evidence' could be distilled down to a single size of effect, with associated statistical precision and that the clinical relevance of this result could be determined eg a pooled relative risk and confidence interval obtained through meta-analysis. The evidence level , designated according to the hierarchy (Table (Table1), 1 ), assessed the likelihood that the 'body of evidence' producing this single size of effect was affected by bias.

It became clear on applying this schema that the available evidence-base for clinical practice guidelines and health technology assessments was often not amenable to meta-analysis. Thus statistical synthesis for each of the outcomes of interest into one estimate of effect, with associated statistical precision and determination of clinical relevance, was often not possible. As a consequence, in practice, the dimensions of evidence were often applied to individual studies and were complemented with a narrative synthesis of the overall findings from the body of evidence. The difficulty with this approach was that the original hierarchy of evidence was not designed, nor worded, to refer to the strength of the evidence obtained from individual studies.

Further, the hierarchy was designed to assess evidence from intervention studies that evaluated therapeutic effectiveness. It was therefore not appropriate for assessing studies addressing diagnostic accuracy, aetiology, prognosis or screening interventions. The study designs best suited to answer these types of questions are not always the same, or presented in the same order, as that given in the original NHMRC hierarchy of evidence. It was clear that an alternative approach to appraising evidence was needed.

The NHMRC therefore created a working party of clinical practice guideline developers, health technology assessment producers and methodologists (the Working Party) to develop a revised hierarchy of evidence for individual studies (first stage) which addressed these issues, as well as a method for appraising the body of evidence (second stage) that could be used by guideline developers and others.

The objective of the first stage was to create a framework that aligned as closely as possible with the original evidence hierarchy – to minimise confusion for current users and maintain consistency with previous use of the hierarchy – but which could also rank individual studies addressing questions other than therapeutic effectiveness. Due consideration was to be given to methods used by other organisations to develop "levels of evidence", in order to minimise duplication of effort.

Recognising the need for an updated hierarchy of evidence, a review was conducted of existing frameworks for assessing non-randomised and non-interventional evidence that are used by Health Technology Assessment (HTA) agencies and guideline developers world-wide [ 10 ]. This internal report commissioned by the NHMRC, and conducted by HTanalysts, provided a resource for the NHMRC and the Working Party to enable revision of the current hierarchy of evidence. The aim was to adapt, if possible, an existing evidence hierarchy or hierarchies.

The report searched for comprehensive evidence frameworks that incorporated non-intervention evidence via HTA and Guideline group websites that were identified through the membership of the International Network of Agencies for Health Technology Assessment (INAHTA) and the Guidelines International Network (GIN) (see Appendix). Bibliographies of identified publications were examined and targeted Medline/EMBASE searches were conducted. Frameworks were included if they were published in English, were developed by a reputable HTA or guideline agency, and contained guidance on at least one of the methodological processes involved in undertaking an evidence-based assessment (Guideline, HTA or systematic review).

The identified frameworks were then used to inform the revision of the NHMRC evidence hierarchy. Six key factors were considered integral to this revision process, specifically that:

1. the hierarchy addressed all types of questions and was not limited to treatment effectiveness alone;

2. the levels I-IV were maintained and aligned as closely as possible with the current NHMRC (treatment effectiveness) hierarchy;

3. the hierarchy related to individual studies rather than a body of evidence (given a multi-factorial method of "grading" the body of evidence was being developed/adapted concurrently via the NHMRC Working Party);

4. the hierarchy remained broadly consistent across types of question;

5. empirical evidence supported the placement of a particular study design in the evidence hierarchy wherever possible – that is, the relationship between study design and bias for each clinical or research question had been assessed empirically; or if not, there were good theoretical grounds for such placement in the hierarchy; and

6. subjective terms regarding the "quality" of studies eg "well designed", "properly designed" would be removed. The level of evidence would be assessed on the basis of study design characteristics alone. Determination of the overall "quality" of the study would be independently determined using appropriate – and validated, where possible – checklists suitable for each study design and question.

The "Levels" subgroup of the Working Party addressed each of these criteria while drafting a revision of the evidence hierarchy. This first iteration of the hierarchy was slightly modified after consultation with other methodological experts within the wider Working Party. A second iteration of the hierarchy was presented to Australian and New Zealand evaluators undertaking health technology assessments for the Australian Medical Services Advisory Committee (MSAC). Other international experts on evidence appraisal were contacted and provided feedback on the hierarchy. These suggestions were discussed and some substantial revisions – particularly concerning the diagnostic accuracy evidence hierarchy – were incorporated into a version of the hierarchy that was suitable for piloting.

The hierarchy was piloted by NHMRC clinical practice guideline developers and health technology assessment evaluation groups in Australia and New Zealand from November 2004 until June 2007. Public consultation throughout this period was invited through the medium of international conferences and workshops – specifically the Cochrane Colloquium and the Health Technology Assessment international (HTAi) conference [ 11 - 13 ] – and through the NHMRC website. With the website, a feedback form allowing free text responses to a series of questions regarding the utility and adaptability of the revised hierarchy was provided, along with a section for suggested methods for improving the hierarchy. The hierarchy was amended and a further pilot stage was then conducted from February 2008 to February 2009. In total, approximately a dozen responses were submitted through the website, predominantly by individuals or organisations that had trialled the new evidence hierarchy.

Identifying possible frameworks for adaptation

The 2004 report commissioned by the NHMRC identified 18 evidence frameworks that were relevant for clinical evaluation of non-interventional evidence at that time [ 10 ]. Three of the evidence evaluation frameworks were found to use a hierarchy that related to questions other than treatment or intervention effectiveness. The National Institute for Clinical Excellence (NICE) provided a hierarchy that used levels of evidence for assessment of therapeutic effectiveness (based on those developed by the Scottish Intercollegiate Guidelines Network – SIGN) as well as for diagnostic accuracy [ 14 ]. The National Health Service Centre for Reviews and Dissemination (NHS CRD) used a framework that included levels of evidence for assessing questions of effectiveness, diagnostic accuracy, and efficiency [ 15 ]. Finally, the Centre for Evidence Based Medicine (CEBM) hierarchy included levels of evidence for assessing questions of therapy/prevention and aetiology/harm, prognosis, diagnosis, differential diagnosis/symptom prevalence, and economic and decision analyses [ 16 ].

In terms of addressing different types of questions, the CEBM framework was found to be the most comprehensive and a suitable evidence hierarchy upon which to model the revised NHMRC hierarchy of evidence, although all three provided useful information.

The revised NHMRC hierarchy

Each of the six key factors considered integral to a revised NHMRC evidence hierarchy were adopted. Five separate research areas were addressed – interventions, diagnostic accuracy, prognosis, aetiology and screening.

A greatly expanded table was created, largely based on the design of the CEBM framework, which included five separate columns for each of the different research areas (see Additional file 1 ). However, even though the CEBM layout was very closely followed in the revised NHMRC hierarchy, the number of research questions addressed and description of studies did differ markedly from the CEBM framework. Empirical evidence of study design biases and epidemiological theory were used to rank the study designs within each research area. It was suggested that when referring to studies designated a level of evidence according to the revised NHMRC hierarchy, both the level and corresponding research area or question should be used eg. level II intervention evidence; level IV diagnostic evidence; level III-2 prognostic evidence.

To support users of the revised NHMRC evidence hierarchy, explanatory notes (see Additional file 1 ) and a glossary of study designs and terminology (see Additional file 2 ) were developed and adapted from the NHMRC handbooks [ 1 , 2 , 5 - 9 ]. The explanatory notes provide the context for the evidence hierarchy, with guidance on how to apply and present the levels of evidence. The glossary provides a definition of each of the given study designs.

The revised NHMRC hierarchy of evidence largely addresses the issues which brought about its development. This hierarchy was developed using a combination of evidence, theory and consultation. The Working Party was able to successfully achieve its aim of providing a practical and usable tool for evidence-based healthcare practitioners and researchers. A number of special considerations were addressed in the development of this revised hierarchy, and some limitations were acknowledged when designing the hierarchy.

Limitations

The evidence-base underpinning the development of a hierarchy such as this is limited. For intervention research questions there were some studies and a systematic review showing the degree of bias associated with observational and non-randomised studies, in comparison to randomised controlled trials [ 17 - 19 ]. However, for diagnostic research questions, at the time of developing the hierarchy we were aware of only one study on design-related bias associated with diagnostic studies [ 20 ]. In instances where the evidence was lacking to determine placement of the study design in the hierarchy, the CEBM evidence framework was used, along with epidemiology texts [ 21 ] and consensus expert opinion.

An evidence hierarchy addressing individual studies, alone, cannot provide interpretation of the results of a 'body of evidence' and the various contextual factors that can impinge on the interpretation of results (eg external validity/applicability). The 'Working Party' believes that any assessment of evidence underpinning a question involves three steps:

1. determine the level of evidence of individual studies addressing that question and rank the evidence accordingly;

2. appraise the quality of the evidence within each ranking using basic clinical epidemiology and biostatistical principles outlined in widely available critical appraisal checklists and tools; and

3. synthesise the findings from steps 1 and 2 and give greatest weight to the highest quality/highest ranked evidence. After including consideration of contextual factors, make a clear and transparent decision or recommendation regarding the strength and applicability of the findings from the body of evidence, and grade that recommendation.

Steps 1 and 2 are addressed in this paper. Step 3 was undertaken by the NHMRC Working Party through creating a process and system for classifying and grading the body of evidence that takes into account dimensions other than the internal validity of the studies – an issue which has received similar attention in other countries [ 22 , 23 ]. Progress on other grading systems to date has primarily centred on therapeutic safety and effectiveness research questions [ 24 , 25 ], although there have been recent moves towards explicitly incorporating diagnostic evidence [ 26 ]. The NHMRC Working Party has developed a multi-dimensional system to grade the evidence and develop recommendations in a user-friendly manner but which also addresses various types of research question (through use of this revised NHMRC evidence hierarchy as an intermediary step). This "grading" process is reported elsewhere and will be the subject of a subsequent publication [ 3 , 4 ].

While the revised hierarchy described in this paper has greatly expanded the types of studies that can be assigned a level of evidence, it does not cover qualitative research or economic analysis. There are existing hierarchies of evidence for economic analysis, although it is unclear if the methodological basis for the ranking within these hierarchies is supported by evidence and theory [ 15 , 16 ]. Should there be an expressed need to expand the revised NHMRC hierarchy to include economic analysis, this can occur when the NHMRC handbooks are updated.

Methods for synthesising qualitative research evidence are still being developed by groups such as the Cochrane Collaboration [ 27 ] and others [ 28 , 29 ]. In this context, critical appraisal guides and hierarchies of qualitative evidence have begun to appear in the literature [ 30 ]. A proper consideration of these issues was beyond the scope of this project and outside the methodological expertise of the Working Party. However, this should be addressed by investigators with appropriate expertise in qualitative research methods as part of the NHMRC handbook updates.

Special considerations

1. systematic reviews of lower level evidence.

In general, the Working Party took the view that systematic reviews should only be assigned a level of evidence as high as the studies contained therein. Even the best quality systematic reviews will still only be able to answer a research question on the basis of the evidence it has collated and synthesised. Thus any overall conclusions will be affected by the internal validity of the primary research evidence included. However, consistent with the original NHMRC hierarchy of evidence, Level I of the revised hierarchy was retained as a systematic review of all relevant level II studies, recognising that meta-analysis of Level II studies can increase the precision of the findings of individual Level II studies [ 31 ].

2. Studies of diagnostic test accuracy

The effectiveness of a diagnostic test or a screening test requires either direct evidence ie the impact of the test on patient health outcomes (outlined in the 'Intervention' and 'Screening' columns, respectively, in the revised hierarchy) [ 26 ] or, if certain conditions are fulfilled, the linking of evidence of diagnostic test accuracy (assessed using the 'Diagnostic accuracy' column in the hierarchy) with evidence of change in management and the likely effect of that change in management on patient health outcomes (assessed using the 'Intervention' column in the revised hierarchy) [ 32 , 33 ].

The development of levels of evidence for studies of diagnostic accuracy proved to be more difficult than for the other types of research question. In studies of diagnostic accuracy the basic study design is cross-sectional, in which all participants receive both the index test and the reference standard. In order to rank the validity of each individual study's results it was found that a more specific discussion of study design was required. To aid with the interpretation and ranking of studies comprehensive explanatory notes were developed. To some extent the degree of bias introduced by a particular study design feature is dependent upon both the disease and the diagnostic test context under investigation. Well-developed critical appraisal skills of the reviewers of diagnostic test interventions are therefore essential. Methods for assessing diagnostic test accuracy by systematic review and meta-analysis have been progressing over a relatively short period of time (especially compared with studies of therapeutic effectiveness) [ 34 - 37 ]. As this methodology matures, the descriptive nature of the 'Diagnostic accuracy' levels in the revised hierarchy may no longer be required, as study designs in which bias is minimised are recognised (and possibly even named) as is currently the case with studies of therapeutic effectiveness.

3. Correct classification of the research question

One other difficulty has been noted with use of the evidence hierarchy. The difficulty is not with the study designs or the ranking of the study designs, but rather with distinguishing between an aetiological and prognostic research question – and thus correct use of the relevant hierarchy. Both aetiology and prognosis relate to an identification of risk factors for an outcome and so the relevant study designs are quite similar. The key when determining if a research question is aetiological or prognostic is to identify the population of interest. For prognostic questions, all the population has the condition/disease and the aim is to determine what factors will predict an outcome for that population (eg survival) [ 2 ]. For example, "What are the risk factors for suicide in adolescent depression?" These factors can be causal (eg a treatment modality), effect modifiers (eg age) or just associations or markers. For aetiology questions, the key is ensuring the population of interest do not or did not have the condition/disease at some point in time, so that causality of the risk factor can be determined [ 2 ]. For example, "What are the risk factors for adolescent depression?" The explanatory notes to the hierarchy cannot make this distinction between aetiology and prognosis completely clear because of the degree of overlap in the relevant study designs.

4. Assessment of study quality

The revised hierarchy of evidence is intended to be used as just one component in determining the strength of the evidence; that is, determining the likelihood of bias from the study design alone. This component is seen as a broad indicator of likely bias and can be used to roughly rank individual studies within a body of evidence. However, study quality within each of the levels of evidence needs to be assessed more rigorously. The Working Party believes that there are so many factors affecting the internal validity of study results (e.g. bias, confounding, results occurring by chance, impact of drop-outs), with different factors affecting different study designs, that a proper assessment of study quality can only occur with the use of an appropriate and/or validated checklist suitable for each study design or research question [ 2 , 15 , 25 , 37 , 38 ]. In the accompanying documentation to the revised evidence hierarchy, suggestions have been made as to the appropriate checklists for a formal critical appraisal of studies addressing the different types of research question [ 4 ].

5. Ethical considerations

The impact of ethics on the hierarchy of study designs was acknowledged in the revised evidence hierarchy. Separate columns for aetiology and intervention research questions were produced in order to address trial feasibility and ethical issues. Explanatory notes appended to the hierarchy indicate that if it is possible and/or ethical to determine a causal relationship using experimental evidence, then the 'Intervention' hierarchy of evidence should be used. However, if it is only possible and/or ethical to determine a causal relationship using observational evidence (for example if it is not ethical to allocate groups to a potentially harmful exposure such as nuclear radiation), then the 'Aetiology' hierarchy of evidence should be used [ 39 , 40 ]. In the latter scenario, the highest level of evidence that could be used to address the question would be observational and not experimental.

6. Assessment of harms/safety

There is guidance in the explanatory notes about how to deal with the evaluation of comparative harms and safety in the research area of interest. Assessment of comparative harms/safety should occur according to the hierarchy presented for each of the research questions, with the proviso that this assessment occurs within the context of the topic being assessed. Some harms (as well as some effectiveness outcomes) are rare and cannot feasibly be captured within randomised controlled trials [ 41 , 42 ], in which case lower levels of evidence may be the only type of evidence that is practically achievable; physical harms and psychological harms may need to be addressed by different study designs [ 43 ]; harms from diagnostic testing include the likelihood of false positive and false negative results [ 44 , 45 ]; harms from screening include the likelihood of false alarm and false reassurance results [ 46 ].

No single evidence-framework can address all of the safety and effectiveness issues associated with different research areas. The aim of the explanatory note was to explicitly recognise that these differences will occur and to adapt the hierarchy where necessary.

Given the extensive pilot process – four years – this new evidence hierarchy is now the standard for judging "levels of evidence" for the purposes of health technology assessment and clinical practice guideline development in Australia.

Although this broad ranking tool for assessing study quality is intended for use as an intermediary step within the new NHMRC system to grade the body of evidence addressing a clinical, research or policy question [ 4 ], it can be applied within existing grading systems eg GRADE [ 47 ], SIGN [ 25 ] with the benefit of allowing a ranking of evidence that addresses research questions or areas other than therapeutic effectiveness.

This tool is particularly advantageous for structuring a narrative meta-synthesis of results in an evidence report or health technology assessment. Studies and study results can initially be ranked by study design (evidence level) using the revised evidence hierarchy, and then be further ranked within each evidence level with the use of appropriate and validated quality appraisal checklists. A grading of the body of evidence can then be applied, if relevant.

Competing interests

Meeting attendance fees for this methodological work were paid to the authors by the National Health and Medical Research Council (NHMRC), a not-for-profit research organisation funded by the Australian Government Department of Health and Ageing. One of the functions of the NHMRC is to develop and disseminate health publications to health professionals and consumers in Australia. They produce health advisories, evidence-based clinical practice guidelines and methodology publications.

Authors' contributions

TM instigated the revision of the original NHMRC evidence hierarchy, co-developed the revised evidence hierarchy, wrote the explanatory notes and glossary, drafted the manuscript, and incorporated the feedback received on both the hierarchy and the manuscript. AW conducted the review of international frameworks assessing non-randomised or non-interventional evidence (in conjunction with Dr Kristina Coleman and Dr Sarah Norris), co-developed the revised evidence hierarchy, and contributed to the development of the manuscript. RT co-developed the revised evidence hierarchy and contributed to the development of the manuscript. All authors read and approved the final manuscript.

Searches were conducted in June 2004. Enquiries regarding the search strategies should be directed to the Evidence Translation Section, National Health and Medical Research Council, Canberra, ACT, Australia.

Pre-publication history

The pre-publication history for this paper can be accessed here:

http://www.biomedcentral.com/1471-2288/9/34/prepub

Supplementary Material

Additional File 1 NHMRC Evidence Hierarchy: designations of 'levels of evidence' according to type of research question (including explanatory notes) . Revised NHMRC evidence hierarchy and explanatory notes.

Additional File 2 Study design glossary (alphabetic order) . Description of study designs included in the revised NHMRC evidence hierarchy.

Acknowledgements

We would like to thank the other members of the NHMRC Guideline Assessment Working Party for their input – specifically, Kristina Coleman, Sarah Norris, Karen Grimmer-Somers, Susan Hillier, Philippa Middleton, and Janet Salisbury. We would also like to acknowledge the efforts of Janine Keough and Chris Gonzalez, formerly of the NHMRC Health Advisory Section. We appreciated the feedback provided to the NHMRC by Paul Glasziou, Brian Haynes, Andrew Oxman, Nicki Jackson and those who submitted suggestions via the website. The suggestions provided by Sally Lord and Les Irwig were particularly helpful. We would also like to thank Janet Hiller and Phil Ryan for providing internal peer review and Mike Clarke and Myfanwy Jones for their very useful suggestions during external peer review of the manuscript.

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The University of Chicago The Law School

Global human rights clinic—significant achievements for 2023-24.

The Global Human Rights Clinic (GHRC) students continue to advance justice and address the inequalities and structural disparities that lead to human rights violations worldwide using diverse tactics and interdisciplinary tools. Over the past year, students and clinic director Anjli Parrin—who joined the faculty permanently in October 2023—worked in teams to promote human rights around the world. In particular, the GHRC supported justice efforts in the context of conflict and related to mass atrocities; the investigation and prevention of unlawful killings globally; the rights of missing migrants; the right to health; climate justice; and the right to equality and non-discrimination. Select work from each of these strands is described below.

Justice in Conflict: Supporting Atrocity Investigations in The Gambia and Central African Republic

The GHRC partners with civil society organizations and multidisciplinary scientific experts to investigate war crimes and mass atrocities, and advance justice in the context of conflict. Over this past year, the GHRC supported effective investigations in the Central African Republic and the Gambia. In addition, the Clinic worked with grassroots civil society and victims’ associations in both countries to advance critical human rights.

Central African Republic

In the Central African Republic (CAR), protracted violence and conflict has had devastating impacts on the civilian population. Civilians have borne the brunt of grave human rights violations, and the country remains one of the poorest in the world. The GHRC supported judicial authorities to carry out complex investigations of alleged mass atrocities committed during armed conflict in the country. Students worked alongside lawyers and scientific experts to conduct detailed factfinding, prepare legal memos on evidence collection and preservation, and support the creation of investigation files of human rights abuses.

Further, the GHRC alongside the Columbia Law School Smith Family Human Rights Clinic, partnered with CAR civil society, which is significantly under-funded and under-resourced, and therefore frequently shut out of international human rights forums and subject to attacks and threats domestically. We worked with two organizations—the Collectif des Organisations Musulmanes de Centrafrique (COMUC), an umbrella network of Muslim civil society, and the Association des Femmes Juriste de Centrafrique (AFJC), a women’s lawyers’ organization, and one of the largest providers of legal aid in the country—to document and advocate for the rights of religious minorities and women at the United Nations Human Rights Council. Students supported these organizations to:

Launch a major human rights report on the right to freedom of religion and belief, and non-discrimination of religious minorities in CAR. This report documents violations of the right to life, arbitrary detention, freedom of movement, legal recognition, health, and education, and was launched in Geneva in December 2023.
Carry out advocacy before the United Nations Human Rights Council in Geneva, as part of CAR’s Universal Periodic Review, a unique process of the Council whereby States’ human rights records are reviewed every five years. Students supported advocates from COMUC and AFJC to prepare reports on the human rights situation, present at a pre-session for the review in Geneva, and to meet diplomatic missions to inform them about the human rights situation in the country. The clinic’s support to national civil society ensured that they had access to this important international advocacy forum. The civil society reports can be accessed at the UN Office of the High Commission for Human Rights website (for a summary, see, A/HRC/WG.6/45/CAF/3 ).

In the Gambia, a military regime run by autocrat Yahya Jammeh committed scores of human rights abuses between 1994 and 2016, including arbitrary detentions, extrajudicial killings, and enforced disappearances. Following the overturning of the Jammeh regime, a truth commission was created to understand what happened during the dictatorship, and a special prosecution office is being set up. Families of those killed and disappeared are searching for answers as to the fate of their loved ones.

In partnership with the African Network Against Extrajudicial Killings and Enforced Disappearances (ANEKED) Gambia chapter, the Gambian Ministry of Justice, and the Argentine Forensic Anthropology Team, GHRC students supported efforts to advance justice and the search for missing persons in the Gambia. In particular, building on an assessment of the forensic and international criminal system conducted last year, the GHRC worked with civil society to carry out factfinding related to a key mass atrocity case. Additionally, in the Fall, the GHRC will work with ANEKED to expand its transitional justice and memory curriculum, so that young persons in the Gambia and globally learn about the process for truth and justice in the country.

Extrajudicial Executions: Preventing and Investigating Unlawful Deaths Globally

The GHRC provided strategic support to Morris Tidball-Binz, the United Nations Special Rapporteur on Extrajudicial, Summary, or Arbitrary Executions, and a leading independent human rights expert appointed by the United Nations to advise on the issue of unlawful killings from a thematic perspective. The Special Rapporteur procedures are a key pillar through which human rights is advanced at the UN. As part of their mandate, Special Rapporteurs undertake country visits, conduct annual thematic studies, and act on individual cases of reported violations by sending communications to States and international authorities. As of June 2024, Tidball-Binz joined the University of Chicago Pozen Family Center for Human Rights as a visiting senior research associate, where he will engage with and conduct joint research alongside Pozen Center and GHRC students.

In particular, the GHRC supported the Special Rapporteur with:

Preparation for his country visit to Ukraine in May 2024. GHRC students conducted detailed research, factfinding, and analysis of concerns relating to unlawful killings in Ukraine, producing background research about the human rights situation prior to as well as during the ongoing escalation in hostilities. The research covered legislative and policy structures, key crosscutting concerns, emblematic cases, and positive developments. During the Special Rapporteur’s actual time in-country, GHRC students provided remote, ongoing support as required.
Support in the research and drafting of his thematic report on the protection of the dead from a human rights perspective. GHRC students conducted factfinding, expert interviews, and legal analysis to inform the Special Rapporteur’s thematic report on protection of the dead, which was presented to the UN Human Rights Council on June 26, 2024 ( A/HRC/56/56 ). The UN Special Rapporteur acknowledged the contributions of the GHRC (video, remarks referencing the GHRC at 31:30).

Missing Migrants: A Forensic Response for African Missing Migrants in Southwest Europe

Thousands of Africans go missing each year attempting to cross international borders in search of safety and better opportunities. Despite the broad recognition among states of the importance and need to address the situation of missing migrants, there is a lack of formal coordination and procedures among all relevant stakeholders relating to missing migrants, and in many instances, even within a country’s government, there is a lack of information sharing. For families searching for the fate and whereabouts of their loved ones, the uncertainty is devastating, often leaving them in limbo.

In partnership with the Immigrants’ Rights Clinic (IRC) and the Argentine Forensic Anthropology Team, the GHRC is supporting efforts to identify missing migrants traveling from Africa to South-West Europe. Over this course of this academic year, GHRC/IRC students:

Researched migration patterns in key departure and transit countries in Africa, focusing on migrants leaving from the Gambia, Senegal, Morocco, and Tunisia. Additionally, students researched migration arrival patterns in Spain.
Commenced an analysis of the existing legal frameworks governing the rights of missing migrants, and laws that pertain to transnational exchange of information of missing migrants. This analysis will be further developed and published next academic year.
Prepared to carry out travel to the Gambia, Senegal, Tunisia, and Morocco, including identifying key stakeholders in each country from civil society, state institutions, and intergovernmental institutions.

Advancing the Right to Health Globally

GHRC students work to address violations of the right to health globally. We do so in two key areas—by working with Indigenous groups globally to reinterpret the international human right to health in accordance with Indigenous knowledge systems; and to support the realization of the right to health in the context of armed conflict.

Indigenous rights to health

In partnership with Human Rights Watch and Indigenous groups in South Africa, the Navajo Nation, and Guåhan (Guam), GHRC students are working to tackle systemic harms within global health and understand the impact of colonial determinants on health outcomes. This academic year, students worked to finalize a human rights report on the impact of US military buildup in Guåhan on Indigenous CHamoru medicinal and healing practices (the military currently controls approximately one-third of land on Guåhan). This report will be released in the Fall of 2024. Further, GHRC students supported Indigenous groups in South Africa and the Navajo Nation to document violations of the right to health in their lands.

Drawing upon his research through the GHRC, undergraduate student Elijah Jenkins was selected to receive the prestigious Stamps Scholarship , which will support him to undertake additional research in Guåhan. As a CHamoru student, Jenkins will deepen his understanding of and research into the impact of colonialism on the peoples of Guåhan and will continue to be supported by the GHRC.

Attacks on healthcare in conflict

The GHRC partnered with the University of Chicago’s Pritzker School of Medicine to document, research, and support legal claims of violations of the right to health in the context of the ongoing conflict in Israel and Palestine. This project is taking place with the support and partnership of the Heath and Vascular Hospital at the Public Aid Society in Gaza. GHRC law students and Pritzker School medical students teamed up to conduct interviews with doctors who have recently traveled to Gaza, conduct open-source research into violations of the right to health, and analyze the applicable international humanitarian law governing protection of medical establishments and personnel. The team is currently preparing joint submissions to legal and quasi-judicial bodies.

Bridging the Chasm Between Law, Science, Technology and Narrative to Advance Climate Justice

While climate change is having a devastating impact across the planet, the harms are not experienced equally. Those on the frontlines of the climate crisis are frequently those who have contributed least to climate harms—including Indigenous groups, individuals living in small island nations, young people, and communities across the Global South. Coalitions of young people, including the Pacific Island Students Fighting Climate Change (PISFCC) and the World’s Youth for Climate Justice (WY4CJ), are leading the right to ensure a livable present and future.

In March 2023, the PISFCC succeeded in getting a historic resolution adopted, asking the International Court of Justice—the World’s Court—to rule on what the obligations of States are to protect the climate, and what the consequences are for the world’s biggest violators. Ahead of the ICJ oral hearings, GHRC is partnering with PISFCC, WY4CJ, visual investigations experts SITU Research , and artist Suneil Sanzgiri, to create a fifteen-minute film that weaves together the stories of young people and the impacts of climate harm through testimony, historical and contemporary documentation, and climate science. The film will debut at the Pinakothek der Moderne museum as part of the upcoming exhibition, Visual Investigations: between Advocacy, Journalism, and Law , opening October 10, 2024 in Munich, Germany.

Advancing Equality: Resisting Discriminatory Laws in Uganda and Globally

Discriminatory laws impact the ability of sexual and gender minorities, as well as other vulnerable groups, to access basic rights. Recently, several countries have passed discriminatory laws, including ones criminalizing homosexuality with extraordinarily punitive sentences. GHRC students work alongside civil society organizations in Uganda and around the world to challenge unfair laws and policies. This academic year, students:

Partnered with Chapter Four Uganda and the Makerere University Human Rights and Peace Centre to develop a strategy to challenge discriminatory provisions in the survivor’s benefit clause of the National Social Security Fund Act. In March 2024, GHRC students traveled to Uganda to host the first of its kind moot court competition around this provision. Students partnered with Ugandan colleagues to prepare their arguments, and following the event met with the Minister of Justice to advocate for changes in the law. Currently, students are preparing a joint white paper on the issue, which will be published over the summer of 2024.
In partnership with Stanford Law School International Human Rights and Conflict Resolution Clinic, GHRC students supported major NGOs in countries where new restrictions on sexual orientation and gender identity had been passed to analyze the restrictions and publish public-facing advocacy documents explaining their implications.
Supported the UN Special Rapporteur on Extrajudicial, Summary or Arbitrary Executions with research and legal analysis of LGBTQI+ killings, ahead of a thematic report which he will present to the UN General Assembly in October 2024.

Student Post-Graduate Fellowships

Additionally, GHRC graduating students obtained prestigious fellowships to pursue public interest work post-graduation. In 2023, Nico Thompson Lleras and Marin Murdock both received fellowships to work at Reprieve’s Unlawful Detention program and International Coalition of Sites of Conscience’s Global Initiative for Justice, Truth, and Reconciliation. In 2024, graduating student Bryant King will join the Clooney Foundation for Justice as a legal fellow, and Elisa Epstein received the Equal Justice Works Fellowship to support a two-year fellowship at the American Civil Liberties Union (ACLU).

IMAGES

NHMRC Hierarchy of Evidence
National Health and Medical Research Council hierarchy of evidence
National Health and Medical Research Council Level of Evidence Matrix
Levels of evidence by National Health and Medical Research Council
NHMRC evidence hierarchy: designations of 'lev- els of evidence
Australian National Health and Medical Research Council Evidence

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PDF APPENDIX F: Levels of evidence and recommendation grading
NATIoNAl hEAlTh AND mEDICAl rESEArCh CouNCIl 47 Appendix F: Levels of evidence and recommendation grading Grading of recommendations8 Grade Description A Body of evidence can be trusted to guide practice B Body of evidence can be trusted to guide practice in most situations
Identifying the evidence
6.1. Be informed by well conducted systematic reviews. 6.2. Consider the body of evidence for each outcome (including the quality of that evidence) and other factors that influence the process of making recommendations including benefits and harms, values and preferences, resource use and acceptability.
Guidelines
NHMRC guidelines are intended to promote health, prevent harm, encourage best practice and reduce waste. They are developed by multidisciplinary committees or panels that follow a rigorous evidence-based approach. NHMRC guidelines are based on a review of the available evidence, and follow transparent development and decision making processes.
PDF NHMRC additional levels of evidence and grades for recommendations
The National Health and Medical Research Council (NHMRC) in Australia has, over recent years, developed a suite of handbooks to support organisations involved in the development of evidence- ... Level of evidence: Each study design is assessed according to its place in the research
Global Health Evidence Evaluation Framework [Internet]
These levels of evidence apply only to studies of assessing the accuracy of diagnostic or screening tests. To assess the overall effectiveness of a diagnostic test there also needs to be a consideration of the impact of the test on patient management and health outcomes (Medical Services Advisory Committee 2005, Sackett and Haynes 2002).
5.2 The Evidence Hierarchy
The following image represents the hierarchy of evidence provided by the National Health and Medical Research Council (NHMRC). 1 Most experts agree that the higher up the hierarchy the study design is positioned, the more rigorous the methodology and hence the more likely it is that the study design can minimize the effect of bias on the ...
Research Guides: Systematic Reviews: Levels of Evidence
From the National Health and Medical Research Council (NHMRC) of Australia. ... The hierarchy of evidence (also known as the evidence-based pyramid) is depicted as a triangular representation of the levels of evidence with the strongest evidence at the top which progresses down through evidence with decreasing strength. At the top of the ...
Levels and Grades of Evidence • LITFL • CCC Research
The following is the designation used by the Australian National Health and Medical Research Council (NHMRC): Level I. Evidence obtained from a systematic review of all relevant randomised controlled trials. Level II. Evidence obtained from at least one properly designed randomised controlled trial. Level III-1.
Levels of Evidence in Medical Research
The model is attributed to the National Health and Medical Research Council. NHMRC levels of evidence and grades for recommendations for developers of guidelines. Retrieved from University of Canberra Library. Turner M. "Evidence-Based Practice in Health". 2014. Retrieved from University of Canberra website. Hariton E, Locascio JJ.
Levels of Evidence
Not all evidence is the same. Clearly, results from a systematic review of well conducted double-blind randomised controlled trials are much more reliable than anecdotal opinion.. NHMRC Levels of Evidence. The following is the designation used by the Australian National Health and Medical Research Council (NHMRC) [1]: Level I
Hierarchy of Evidence
The following image represents the hierarchy of evidence provided by the National Health and Medical Research Council (NHMRC). 1 Most experts agree that the higher up the hierarchy the study design is positioned, the more rigorous the methodology and hence the more likely it is that the study design can minimise the effect of bias on the ...
Assessing certainty of evidence
1. Plan your approach to assessing certainty. The decisions you make around forming the questions and deciding what evidence to include may influence the body of evidence you uncover. This body of evidence may also have a number of limitations. For example, when the quality or certainty of evidence for the body of evidence is low, it may be ...
Levels of Evidence, Quality Assessment, and Risk of Bias: Evaluating
An example of the evolution toward more transparent considerations of internal validity of individual studies within a levels of evidence framework is seen in the progression of the Australian National Health and Medical Research Council (NHMRC) system for evaluating evidence in the development of clinical practice guidelines.
PDF The Hierarchy of Evidence
The Hierarchy of Evidence The Hierarchy of evidence is based on summaries from the National Health and Medical Research Council (2009), the Oxford Centre for Evidence-based Medicine Levels of Evidence (2011) and Melynyk and Fineout-Overholt (2011). Ι Evidence obtained from a systematic review of all relevant randomised control trials.
LEVELS OF EVIDENCE IN MEDICINE
In the current paper, the hierarchies presented are based on those recommended by the National Health and Medical Research Council of Australia. 3 However, there are others 4 and they generally follow the same pattern, being different only in the alphanumeric nomenclature given to the levels of the hierarchy (eg: 1a or IIa etc). While one ...
Levels of Evidence in Medical Research
Levels of evidence (or hierarchy of evidence) is a system used to rank the relative strength of medical studies based on the quality and reliability of their research methods. ... The model is attributed to the National Health and Medical Research Council. "NHMRC levels of evidence and grades for recommendations for guideline developers ...
NHMRC Levels of Evidence
Systematic reviews of lower level evidence present results of likely poor internal validity and thus are rated on the likelihood that the results have been affected by bias, rather than whether the systematic review itself is of good quality. ... National Health and Medical Research Council. Additional levels of evidence and grades for ...
Review article: systematic review of three key strategies ...
The National Health Medical Research Council (NHMRC) Level of Evidence Hierarchy (2009) was applied to included studies. Twenty-one articles met criteria for review. The level of evidence assessed using the NHMRC guidelines of studies ranged from I to IV, with the majority falling into the Level II-2 (n = 6) and III-3 (n = 9) range.
Extending an evidence hierarchy to include topics other than ...
Background: In 1999 a four-level hierarchy of evidence was promoted by the National Health and Medical Research Council in Australia. The primary purpose of this hierarchy was to assist with clinical practice guideline development, although it was co-opted for use in systematic literature reviews and health technology assessments.
National Health and Medical Research Council
Working together to support health and medical research. NHMRC is the Australian Government's primary health and medical research funding agency. With NHMRC support, Australia undertakes outstanding research which has contributed to significant improvements in individual and population health. Read more about ways NHMRC can help.
Civil Rights & Police Accountability Clinic—Significant Achievements
Our Clinic students continue to make a difference in the community, while learning all that it means to be a lawyer. The Federal Civil Rights Consent Decree Governing the Chicago Police Department Years of advocacy by Clinic students and our clients resulted in the 2019 federal civil rights Consent Decree that seeks to remedy the Chicago Police Department's (CPD's) pattern and practice of ...
Yoga: Effectiveness and Safety
Yoga is an ancient and complex practice, rooted in Indian philosophy. It began as a spiritual practice but has become popular as a way of promoting physical and mental well-being. Although classical yoga also includes other elements, yoga as practiced in the United States typically emphasizes physical postures (asanas), breathing techniques (pranayama), and meditation (dyana).
Extending an evidence hierarchy to include topics other than treatment
Background. In 1999 a four-level hierarchy of evidence was promoted by the National Health and Medical Research Council in Australia. The primary purpose of this hierarchy was to assist with clinical practice guideline development, although it was co-opted for use in systematic literature reviews and health technology assessments.
Background
National Health and Medical Research Council . The Handbook replaces NHMRC's A guide to the development, implementation and evaluation of clinical practice guidelines, all associated handbooks and the NHMRC additional levels of evidence and grades for recommendations for developers of guidelines (2009).
News
Data and insights from our health surveys, research and monitoring. Go to section. Quick links. New Zealand Health Survey ... on a series of proposed updates to the regulatory guidelines for people conducting clinical trials for medicines and medical devices. News article ... A review of the evidence on effectiveness of suicide prevention ...
Global Human Rights Clinic—Significant Achievements for 2023-24
The Global Human Rights Clinic (GHRC) students continue to advance justice and address the inequalities and structural disparities that lead to human rights violations worldwide using diverse tactics and interdisciplinary tools. Over the past year, students and clinic director Anjli Parrin—who joined the faculty permanently in October 2023—worked in teams to promote human rights around the ...
Research quality
High quality research that is rigorous, transparent and reproducible contributes to scientific progress, is essential for the translation of outcomes into practical and clinical applications and evidence-based policy, delivers the highest possible value for research investment and promotes community trust in scientific findings.

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Extending an evidence hierarchy to include topics other than treatment: revising the Australian 'levels of evidence'

Adele Weston

Rebecca Tooher

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