The PRISMA Statement on Reporting Principles for Systematic Reviews and Meta-Analyses, published in 2009, was developed to help systematic reviewers transparently report why the review was conducted, the methods employed, and what the authors found. Over the past decade, advances in systematic review methodology and terminology have necessitated updating the guideline. The PRISMA 2020 statement replaces the 2009 statement and includes new reporting guidance that reflects advances in methods for identifying, selecting, evaluating, and synthesizing studies. The structure and presentation of the items have been modified to facilitate implementation. In this article, we present the 27-item PRISMA 2020 checklist, an expanded checklist detailing reporting recommendations for each item, the PRISMA 2020 checklist for abstracts, and revised flowcharts for new reviews and for updating reviews.
Systematic reviews play several critical roles. They can provide syntheses of the state of knowledge in a field, from which future research priorities can be identified; they can address questions that would otherwise go unanswered by individual studies; they can identify problems in primary research that need to be corrected in future studies; and they can generate or evaluate theories about how or why phenomena occur. Systematic reviews generate various types of knowledge for different users of the reviews (such as patients, healthcare professionals, researchers, and policymakers). To ensure that a systematic review adds value to users, authors must prepare a transparent, complete, and accurate account of why the review was conducted, what they did (how studies were identified and selected), and what they found (such as characteristics of included studies and results of meta-analyses). Updated reporting guidelines enable authors to achieve these goals.