The development of the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement, published in 2009, was a landmark step in enhancing the rigour of systematic review reporting and was widely endorsed by the scientific community. However, since its publication there have been many developments in the conduct of systematic reviews. These include new methods to synthesise and present findings, assess risk of bias, register review protocols, and share data, to name a few. Due to these advances, the updated PRISMA 2020 statement has been developed, which may prove to be another key milestone in improving the reporting of systematic reviews.

In the PRISMA 2020 statement, Page and colleagues present an updated 27-item manuscript checklist (with an accompanying explanation and elaboration document), an abstract checklist and a new study flow diagram. While there are a variety of changes from the 2009 publication, noteworthy new or updated recommendations within the PRISMA 2020 reporting items include:

• Full search strategies should be provided for all databases used (item #7).
• Details on how many reviewers screened each record and each report retrieved, whether they worked independently, and if applicable, details of automation tools used in the process should be given (item #8).
• Authors should report how outcomes were defined, which results were sought, and methods for selecting a subset of results from included studies (item #10a).
• Details on study eligibility, preparation of data for synthesis, synthesising and displaying of results, possible causes of heterogeneity, and sensitivity analyses should be reported (item #13a–13f).
• Methods for, and results of, assessment of certainty (or confidence) should be reported in the body of evidence for an outcome (items #15 and #22).
• Authors should list citations of studies that met many but not all of the inclusion criteria (i.e. ‘near-misses’) and explain why they were excluded (item #16b).
• Authors should summarise the characteristics and risk of bias among studies, and present results of all syntheses, heterogeneity analyses, and sensitivity analyses (item #20a–20d).
• Amendments to information provided at registration or in the protocol should be described and explained (item #24a–24c).
• Authors should declare any competing interests (item #26).
• Authors should indicate whether data, analytic code and other materials used in the review are publicly available and where they can be found (item #27).

The PRISMA statement website will include helpful fillable templates of the new checklists to download and complete, and an editable template for each flow diagram. A web-based application that allows users to complete the checklist via a user-friendly interface is also currently under development and may facilitate reporting.

Overall, it is expected that implementation of the PRISMA 2020 statement will enhance the transparency, accuracy, and completeness of systematic review reporting, which should benefit the scientific community involved in developing systematic reviews. Importantly, improved reporting of systematic reviews may also have a downstream benefit for patients by facilitating evidence-based decision-making. It is therefore recommended that authors and writers fully utilise the PRIMSA 2020 statement and associated checklists when developing future systematic reviews. We also encourage journals to update their guidelines to include the completed checklist in their submission requirements for upcoming manuscripts.

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Summary by Josh Lilly PhD from Aspire Scientific

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With thanks to our sponsor, Aspire Scientific Ltd

Reporting guidelines help to ensure quality, consistency and transparency in scientific publications – however, they are not yet available for all types of study or analysis. For example, the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines may be insufficient when data unsuitable for meta-analysis necessitate alternative synthesis methods. Currently, a lack of transparency can leave readers questioning the validity of findings from such analyses, yet this is crucial given that approximately one third of health-related systematic reviews, key to informing healthcare policy, use such methods. The Synthesis Without Meta-analysis (SWiM) guidelines, developed by experienced systematic reviewers and released earlier this year, aim to provide clarity for reporting these important analyses.

The nine-item SWiM checklist for reporting systematic reviews using alternative synthesis methods is intended to be used as an extension to PRISMA.

Key elements are to describe:

• groups used in the synthesis (with a rationale)
• standardised metrics for each outcome and any transformation methods
• synthesis methods
• any criteria used to prioritise results from different studies, for the synthesis or conclusions, with justification
• method(s) used to examine heterogeneity in reported effects
• methods used to assess certainty of the synthesis findings
• graphical and tabular methods used to present the findings and key characteristics used to order the studies
• synthesised findings for each comparison and outcome, and the certainty of those findings
• limitations of the synthesis methods and/or groupings used, and the impact on the conclusions that can be drawn.

While SWiM Principal Investigator Dr Hilary Thomson noted that the guidelines have not been able to address everything captured by the ambiguous term ‘narrative synthesis’, she hopes that they increase transparency in reporting and stimulate further discussion. To learn more about the guidelines, why not access webinars and further resources, or get involved in discussing good practice via the SWiM network.

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Summary by Jo Chapman PhD from Aspire Scientific