Clear reporting in systematic reviews is essential. It gives readers the information to form their own views about how well a review was carried out and how applicable the findings are to their own setting. It also makes the research replicable – one of the defining features of a systematic review. PRISMA stands for Preferred Reporting Items for Systematic Reviews and Meta-analyses. Research by Cynthia Mulrow in the 1980s found major deficiencies in the quality of review reports. This work was the start of an initiative to improve standards in reporting that led an international group of experts to create PRISMA. Decades later, systematic review authors everywhere use the PRISMA statement to make sure that their research is as useful as possible for patients, healthcare professionals, and for their fellow researchers ? .

The PRISMA statement

The PRISMA statement is made up of a checklist and a flow diagram: ☑️  The checklist (see figure 1) sets out the 27 items that must be reported in every review. The items can be checked off the list as they are completed. ➡️  The flow diagram reports the decisions that the review team took as they assessed citations for possible inclusion in the review. It relates to checklist item #16a: “Describe the results of the search and selection process, from the number of records identified in the search to the number of studies included in the review, ideally using a flow diagram.” The PRISMA statement is accompanied by several extensions. These are additional checklists that cover specific types or aspects of systematic reviews: protocols, searching, and scoping reviews, for example. The statement is supported by an explanation and elaboration, which gives the rationale for each checklist item along with useful examples.
Figure 1: A section of the PRISMA checklist, which sets out a minimum set of items for reporting systematic reviews of healthcare interventions

Background to PRISMA 2020

First published in 2009, the PRISMA statement soon became a valued and highly cited resource for authors, journal editors, and peer reviewers alike. PRISMA 2020 reflects more than a decade of user experience and advances in systematic review methods. The authors also hope the changes will improve the uptake of the guideline among researchers. To explain how the updated guideline was developed, it seems fitting to *checks notes* report the methods ?. Ok, here goes: The PRISMA team conducted a literature review, surveyed systematic review methodologists and editors, met in person, and collaborated on multiple drafts until everyone approved the content and wording of the updated guideline. Very meta, right? On a more serious note, Page and colleagues did a much better job of reporting these methods, as we might expect. Before we take a look at what’s new in the updated guideline, the PRISMA 2020 statement also has a lot of useful advice for review teams, including these tips:
  • Refer to the guideline early in the writing process to make sure that information is gathered on all of the items and that nothing is missed ✍?.
  • Consider presenting detailed descriptions of methods in supplementary files, rather than in the review itself ?.