David Moher and colleagues introduce PRISMA, an update of the QUOROM guidelines for reporting systematic reviews and meta-analyses

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Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement

Systematic reviews and meta-analyses have become increasingly important in health care. Clinicians read them to keep up to date with their field,1,2 and they are often used as a starting point for developing clinical practice guidelines. Granting agencies may require a systematic review to ensure there is justification for further research,3 and some health care journals are moving in this direction.4 As with all research, the value of a systematic review depends on what was done, what was found, and the clarity of reporting. As with other publications, the reporting quality of systematic reviews varies, limiting readers' ability to assess the strengths and weaknesses of those reviews.

Several early studies evaluated the quality of review reports. In 1987, Mulrow examined 50 review articles published in 4 leading medical journals in 1985 and 1986 and found that none met all 8 explicit scientific criteria, such as a quality assessment of included studies.5 In 1987, Sacks and colleagues6 evaluated the adequacy of reporting of 83 meta-analyses on 23 characteristics in 6 domains. Reporting was generally poor; between 1 and 14 characteristics were adequately reported (mean = 7.7; standard deviation = 2.7). A 1996 update of this study found little improvement.7

In 1996, to address the suboptimal reporting of meta-analyses, an international group developed a guidance called the QUOROM Statement (QUality Of Reporting Of Meta-analyses), which focused on the reporting of meta-analyses of randomized controlled trials.8 In this article, we summarize a revision of these guidelines, renamed PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses), which have been updated to address several conceptual and practical advances in the science of systematic reviews (Box 1).



Box 1

Conceptual issues in the evolution from QUOROM to PRISMA

Preferred reporting items for systematic reviews and meta-analyses: the PRISMA Statement.

Cochrane Reviews have recently started including the quantity I 2 to help readers assess the consistency of the results of studies in meta-analyses. What does this new quantity mean, and why is assessment of heterogeneity so important to clinical practice? 

Systematic reviews and meta-analyses can provide convincing and reliable evidence relevant to many aspects of medicine and health care.1 Their value is especially clear when the results of the studies they include show clinically important effects of similar magnitude. However, the conclusions are less clear when the included studies have differing results. In an attempt to establish whether studies are consistent, reports of meta-analyses commonly present a statistical test of heterogeneity. The test seeks to determine whether there are genuine differences underlying the results of the studies (heterogeneity), or whether the variation in findings is compatible with chance alone (homogeneity). However, the test is susceptible to the number of trials included in the meta-analysis. We have developed a new quantity, I 2, which we believe gives a better measure of the consistency between trials in a meta-analysis.

Assessment of the consistency of effects across studies is an essential part of meta-analysis. Unless we know how consistent the results of studies are, we cannot determine the generalisability of the findings of the meta-analysis. Indeed, several hierarchical systems for grading evidence state that the results of studies must be consistent or homogeneous to obtain the highest grading.2–4

Tests for heterogeneity are commonly used to decide on methods for combining studies and for concluding consistency or inconsistency of findings.5 6 But what does the test achieve in practice, and how should the resulting P values be interpreted?

A test for heterogeneity examines the null hypothesis that all studies are evaluating the same effect. The usual test statistic …

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Measuring inconsistency in meta-analyses

Systematic review and meta-analysis

Preferred reporting items for systematic reviews and meta-analyses: The PRISMA statement

EDITOR—Scientific evidence on the effectiveness of interventions for drug dependence is increasingly available and should be used to inform policies. Differences between the approaches of the Netherlands and Italy lead us to doubt that this is happening.

Dutch investigators have recently recommended the prescription of heroin to addicts on the basis of two randomised controlled trials.1 The European Monitoring Centre for Drugs and Drug Addiction (the European Union's drug agency) recently stated that “substitution treatment is a key component of a comprehensive approach to drug treatment and can be …

Health policies on drug dependence must be based on scientific evidence

In the framework of a monitoring program of quality of care for breast cancer in general hospitals ongoing in Italy since 1983 we have analyzed the epidemiological profile of oestrogen receptor positi

Oestrogen Receptor Status and Risk Factors for Breast Cancer

Indications for and modes of delivery of adjuvant chemotherapy in early breast cancer were assessed in a group of 353 patients followed within a cohort of 1110 newly diagnosed cases in 54 Italian general hospitals. Among node-positive patients 79 % pre- and 44 % postmenopausal women had the treatment. Only a few node-negative women (10 % pre- and 5 % post-menopausal) were treated. The multidrug combination CMF was by far the most commonly employed (89 %) in its two types: cCMF (the classic combination where cyclophosphamide is given orally on days 1–14 and the two other drugs i.v. on days 1 and 8 every 28 days for either 6 or 12 cycles) to 33 % women and nCMF (the more recent combination where all three drugs are given i.v. on day 1 every 21 days for 12 cycles) to 63 %. The mode of delivery of treatment was consistent with the Italian National Breast Cancer Task Force (F.O.N. Ca. M.) recommendations for the cCMF combination, but the lack of clear guidelines on the use of nCMF led to wide variations in the total number of cycles administered. At present, however, it is hard to establish whether this will have any impact on patients’ outcome. Overall the study suggests that adjuvant chemotherapy for breast cancer has entered general practice and can be satisfactorily delivered at the community level. However, better guidelines need to specify more precisely the treatment indications (i.e. subgroups with greater expected benefits), regimen type (is nCMF still experimental or already standard?) and treatment duration, in view of the present uncertainty about what should be the standard for general practice. The paper finally discusses the feasibility of the treatment comparing general hospitals’ performance with that achieved in controlled clinical trials of adjuvant chemotherapy.

Performance of general hospitals in delivering adjuvant chemotherapy to breast cancer patients

EDITOR—Finding that patients with dyspepsia gain modest benefits from eradication of Helicobacter pylori , Moayyedi et al conclude that this intervention “may be cost effective.”1 This conclusion should be taken with quite a bit of healthy scepticism. They say that one patient benefiting out of 15 treated with antibiotics may represent good value for money, depending on decision makers' willingness to pay for relief of dyspepsia. However, the risks associated with the antibiotic treatment are not taken into account in the economic model used.

The table …

Alessandro Liberati

Papers

Health policies on drug dependence must be based on scientific evidence

Oestrogen Receptor Status and Risk Factors for Breast Cancer

Performance of general hospitals in delivering adjuvant chemotherapy to breast cancer patients

Eradicating Helicobacter pylori in non-ulcer dyspepsia may not be cost effective.

The medical treatment of open-angle glaucoma.