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

Date Published: July 21, 2009

Publisher: Public Library of Science

Author(s): Alessandro Liberati, Douglas G. Altman, Jennifer Tetzlaff, Cynthia Mulrow, Peter C. Gøtzsche, John P. A. Ioannidis, Mike Clarke, P. J. Devereaux, Jos Kleijnen, David Moher

Abstract: Alessandro Liberati and colleagues present an Explanation and Elaboration of the PRISMA Statement, updated guidelines for the reporting of systematic reviews and meta-analyses.

Partial Text: 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].

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.

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 Text S1 for a downloadable template checklist for researchers to re-use) and a four-phase flow diagram (Figure 1; see 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.

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 [13],[14],[15],[16].

We modeled this Explanation and Elaboration document after those prepared for other reporting guidelines [17],[18],[19]. To maximize the benefit of this document, we encourage people to read it in conjunction with the PRISMA Statement [11].

The PRISMA Statement and this document have focused on systematic reviews of reports of randomized trials. Other study designs, including non-randomized studies, quasi-experimental studies, and interrupted time series, are included in some systematic reviews that evaluate the effects of health care interventions [172],[173]. The methods of these reviews may differ to varying degrees from the typical intervention review, for example regarding the literature search, data abstraction, assessment of risk of bias, and analysis methods. As such, their reporting demands might also differ from what we have described here. A useful principle is for systematic review authors to ensure that their methods are reported with adequate clarity and transparency to enable readers to critically judge the available evidence and replicate or update the research.

We developed the PRISMA Statement using an approach for developing reporting guidelines that has evolved over several years [178]. The overall aim of PRISMA is to help ensure the clarity and transparency of reporting of systematic reviews, and recent data indicate that this reporting guidance is much needed [3]. PRISMA is not intended to be a quality assessment tool and it should not be used as such.



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