Education and debate

Meta-analysis Spurious precision? Meta-analysis of observational studies

^a Department of Social Medicine, University of Bristol, Bristol BS8 2PR, ^b Department of Social and Preventive Medicine, University of Berne, CH-3012 Berne, Switzerland

Correspondence to: DrEgger m.egger@bristol.ac.uk

In previous articles we have focused on the potentials, principles, and pitfalls of meta-analysis of randomised controlled trials.^{1 2 3 4 5} Meta-analysis of observational data is, however, also becoming common. In a Medline search we identified 566 articles (excluding those published as letters) published in 1995 and indexed with the medical subject heading (MeSH) term "meta-analysis." We randomly selected 100 of these articles and examined them further. Sixty articles reported on actual meta-analyses, and 40 were methodological papers, editorials, and traditional reviews (1). Among the meta-analyses, about half were based on observational studies, mainly cohort and case-control studies of medical interventions or aetiological associations.

The randomised controlled trial is the principal research design in . . . [Full text of this article]

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