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Systematic Reviews: Explaining

PIECES: Systematic Review Process

Explaining the Findings

In the Explaining stage, the review team will synthesize and contextualize the results.

  • Assess the quality of results for each included study. Consider the appropriateness of the study design to the research objective; risk of bias; quality of intervention; choice of outcome measure; quality of reporting; and any statistical concerns.
  • Position the results of the synthesis into context.
  • Describe the strengths and weaknesses of the studies.
  • Interpret the findings for recommendation, potential harmful effects, or inconclusive data for further investigation.
  • This stage refers to the following items in the PRISMA Checklist for systematic reviews:

    • 12 "Risk of bias in individual studies: Describe methods used for assessing risk of bias of individual studies (including specification of whether this was done at the study or outcome level), and how this information is to be used in any data synthesis." 

    • 13 "Summary measures: State the principal summary measures (e.g., risk ratio, difference in means)." 

    • 14 "Synthesis of results: Describe the methods of handling data and combining results of studies, if done, including measures of consistency (e.g., I2) for each meta-analysis."

    • 15"Risk of bias across studies: Specify any assessment of risk of bias that may affect the cumulative evidence (e.g., publication bias, selective reporting within studies)."

    • 16 "Additional analyses: Describe methods of additional analyses (e.g., sensitivity or subgroup analyses, meta-regression), if done, indicating which were pre-specified."


Moher D, Liberati A, Tetzlaff J, Altman DG, The PRISMA Group (2009). Preferred Reporting Items for Systematic Reviews and Meta-Analyses: The PRISMA Statement. PLoS Med 6(7): e1000097. doi:10.1371/journal.pmed1000097

Risk of Bias Assessment

Risk of Bias Assessment Overview

Risk of bias assessment (alternatively quality assessment or critical appraisal) reduces bias in the final evidence synthesis by establishing transparency in the findings. The review team will often perform a risk of bias assessment for each included study in the review. Individual studies included in a synthesis may introduce biases with flaws in their methodology; study design must be assessed for validity and reliability of findings, as well as any inflation of the intervention's efficacy. Risk of bias assessment is required for systematic reviews with a meta-analysis but may not be required for other types of evidence synthesis. 

The Cochrane Risk of Bias Tool (RoB 2) "is the recommended tool to assess the risk of bias in randomized trials included in Cochrane Reviews" and can be used for risk of bias assessment for randomized controlled trials in non-Cochrane systematic reviews.

To use the revised and most current RoB 2 Tool, please see the RoB 2 Tool website with instructions.

Risk of Bias Assessment in Other Disciplines

To learn more about the specific steps for risk of bias assessment in systematic reviews in human medicine, please see the slides for the Cochrane Training: Assessing Risk of Bias in Included Studies [PDF] presentation. Other areas of research may require different guidelines for different study designs beyond randomized controlled trials. For disciplines outside of human medicine, the Critical Appraisal Skills Programme provides checklists appropriate for various study types.  

Risk of Bias Assessment for Scoping Reviews

Scoping reviews do not typically include a risk of bias assessment. According to PRISMA guidelines, a “key difference between scoping reviews and systematic reviews is that the former are generally conducted to provide an overview of the existing evidence regardless of methodological quality or risk of bias. [...] Therefore, the included sources of evidence are typically not critically appraised for scoping reviews.”

PRISMA Extension for Scoping Reviews (PRISMA-ScR): Checklist and Explanation, Annals of Internal Medicine. 2018

 See the full article for more methodology guidelines specific to scoping reviews.

Quality Assessment and Risk of Bias Tool Repository 

If your evidence synthesis project requires the inclusion of non-RCTs and/or a variety of study designs, consult this repository for help in finding and selecting appropriate risk of bias or quality assessment tools. This repository was created and is maintained by Duke University's Medical Center Library & Archives.

Quality Assessment and Risk of Bias Tool RepositoryLeila Ledbetter and Stephanie Hendren. 2021. Licensed under Attribution-NonCommercial 4.0 International.


Visual Representation of Risk of Bias Assessment

Visual Representation of Risk of Bias Assessment

Risk of bias assessments can be represented in the manuscript as a table. Each included study is identified and compared for several quality criteria appropriate for their particular study design.



If a large number of included studies indicate a high risk of bias, use caution when interpreting results and recommendaitons for your evidence synthesis.  More information can be found in Chapter 8 of the Cochrane Handbook.   

Summary of risk of bias for RCTs, PLOS ONE. 2015


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