The PRISMA Statement for Reporting Systematic Reviews and Meta-Analyses of Studies That Evaluate Health Care Interventions: Explanation and Elaboration

Editor's Note: In order to encourage dissemination of the PRISMA explanatory paper, this article is freely accessible on the Annals of Internal Medicine, PLoS Medicine, and BMJ Web sites. The authors jointly hold the copyright of this article. For details on further use, see the PRISMA Web site (www.prisma-statement.org). Systematic reviews and meta-analyses are essential tools for summarizing evidence accurately and reliably. They help clinicians keep up-to-date; provide evidence for policy makers to judge risks, benefits, and harms of health care behaviors and interventions; gather together and summarize related research for patients and their carers; provide a starting point for clinical practice guideline developers; provide summaries of previous research for funders wishing to support new research (1); and help editors judge the merits of publishing reports of new studies (2). Recent data suggest that at least 2,500 new systematic reviews reported in English are indexed in MEDLINE annually (3). Unfortunately, there is considerable evidence that key information is often poorly reported in systematic reviews, thus diminishing their potential usefulness (36). As is true for all research, systematic reviews should be reported fully and transparently to allow readers to assess the strengths and weaknesses of the investigation (7). That rationale led to the development of the QUOROM (QUality Of Reporting Of Meta-analysis) Statement; those detailed reporting recommendations were published in 1999 (8). In this paper we describe the updating of that guidance. Our aim is to ensure clear presentation of what was planned, done, and found in a systematic review. Terminology used to describe systematic reviews and meta-analyses has evolved over time and varies across different groups of researchers and authors (see Box 1). In this document we adopt the definitions used by the Cochrane Collaboration (9). A systematic review attempts to collate all empirical evidence that fits pre-specified eligibility criteria to answer a specific research question. It uses explicit, systematic methods that are selected to minimize bias, thus providing reliable findings from which conclusions can be drawn and decisions made. Meta-analysis is the use of statistical methods to summarize and combine the results of independent studies. Many systematic reviews contain meta-analyses, but not all. Box 1. Terminology. The QUOROM Statement and Its Evolution Into PRISMA The QUOROM Statement, developed in 1996 and published in 1999 (8), was conceived as a reporting guidance for authors reporting a meta-analysis of randomized trials. Since then, much has happened. First, knowledge about the conduct and reporting of systematic reviews has expanded considerably. For example, The Cochrane Library's Methodology Register (which includes reports of studies relevant to the methods for systematic reviews) now contains more than 11,000 entries (March 2009). Second, there have been many conceptual advances, such as outcome-level assessments of the risk of bias (10, 11), that apply to systematic reviews. Third, authors have increasingly used systematic reviews to summarize evidence other than that provided by randomized trials. However, despite advances, the quality of the conduct and reporting of systematic reviews remains well short of ideal (36). All of these issues prompted the need for an update and expansion of the QUOROM Statement. Of note, recognizing that the updated statement now addresses the above conceptual and methodological issues and may also have broader applicability than the original QUOROM Statement, we changed the name of the reporting guidance to PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses). Development of PRISMA The PRISMA Statement was developed by a group of 29 review authors, methodologists, clinicians, medical editors, and consumers (12). They attended a three-day meeting in 2005 and participated in extensive post-meeting electronic correspondence. A consensus process that was informed by evidence, whenever possible, was used to develop a 27-item checklist (Table 1; see also Table S1, for a downloadable template checklist for researchers to re-use) and a four-phase flow diagram (Figure 1; see also Figure S1, for a downloadable template document for researchers to re-use). Items deemed essential for transparent reporting of a systematic review were included in the checklist. The flow diagram originally proposed by QUOROM was also modified to show numbers of identified records, excluded articles, and included studies. After 11 revisions the group approved the checklist, flow diagram, and this explanatory paper. Table S1. Template checklist Figure S1. Template document Table 1. Checklist of Items to Include When Reporting a Systematic Review (With or Without Meta-Analysis) Figure 1. Flow of information through the different phases of a systematic review. The PRISMA Statement itself provides further details regarding its background and development (12). This accompanying Explanation and Elaboration document explains the meaning and rationale for each checklist item. A few PRISMA Group participants volunteered to help draft specific items for this document, and four of these (DGA, AL, DM, and JT) met on several occasions to further refine the document, which was circulated and ultimately approved by the larger PRISMA Group. Scope of PRISMA PRISMA focuses on ways in which authors can ensure the transparent and complete reporting of systematic reviews and meta-analyses. It does not address directly or in a detailed manner the conduct of systematic reviews, for which other guides are available (1316). We developed the PRISMA Statement and this explanatory document to help authors report a wide array of systematic reviews to assess the benefits and harms of a health care intervention. We consider most of the checklist items relevant when reporting systematic reviews of non-randomized studies assessing the benefits and harms of interventions. However, we recognize that authors who address questions relating to etiology, diagnosis, or prognosis, for example, and who review epidemiological or diagnostic accuracy studies may need to modify or incorporate additional items for their systematic reviews. How To Use This Paper We modeled this Explanation and Elaboration document after those prepared for other reporting guidelines (1719). To maximize the benefit of this document, we encourage people to read it in conjunction with the PRISMA Statement (11). We present each checklist item and follow it with a published exemplar of good reporting for that item. (We edited some examples by removing citations or Web addresses, or by spelling out abbreviations.) We then explain the pertinent issue, the rationale for including the item, and relevant evidence from the literature, whenever possible. No systematic search was carried out to identify exemplars and evidence. We also include seven Boxes that provide a more comprehensive explanation of certain thematic aspects of the methodology and conduct of systematic reviews. Although we focus on a minimal list of items to consider when reporting a systematic review, we indicate places where additional information is desirable to improve transparency of the review process. We present the items numerically from 1 to 27; however, authors need not address items in this particular order in their reports. Rather, what is important is that the information for each item is given somewhere within the report. The PRISMA Checklist Title and Abstract Item 1: Title Identify the report as a systematic review, meta-analysis, or both. Examples Recurrence rates of video-assisted thoracoscopic versus open surgery in the prevention of recurrent pneumothoraces: a systematic review of randomised and non-randomised trials (20). Mortality in randomized trials of antioxidant supplements for primary and secondary prevention: systematic review and meta-analysis (21). Explanation Authors should identify their report as a systematic review or meta-analysis. Terms such as review or overview do not describe for readers whether the review was systematic or whether a meta-analysis was performed. A recent survey found that 50% of 300 authors did not mention the terms systematic review or meta-analysis in the title or abstract of their systematic review (3). Although sensitive search strategies have been developed to identify systematic reviews (22), inclusion of the terms systematic review or meta-analysis in the title may improve indexing and identification. We advise authors to use informative titles that make key information easily accessible to readers. Ideally, a title reflecting the PICOS approach (participants, interventions, comparators, outcomes, and study design) (see Item 11 and Box 2) may help readers as it provides key information about the scope of the review. Specifying the design(s) of the studies included, as shown in the examples, may also help some readers and those searching databases. Box 2. Helping To Develop the Research Question(s): The PICOS Approach. Some journals recommend indicative titles that indicate the topic matter of the review, while others require declarative titles that give the review's main conclusion. Busy practitioners may prefer to see the conclusion of the review in the title, but declarative titles can oversimplify or exaggerate findings. Thus, many journals and methodologists prefer indicative titles as used in the examples above. Item 2: Structured Summary Provide a structured summary including, as applicable: background; objectives; data sources; study eligibility criteria, participants, and interventions; study appraisal and synthesis methods; results; limitations; conclusions and implications of key findings; funding for the systematic review; and systematic review registration number. Example Context: The role and dose of oral vitamin D supplementation in nonvert