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Education And Debate

Meta-analysis: Potentials and promise

BMJ 1997; 315 doi: (Published 22 November 1997) Cite this as: BMJ 1997;315:1371
  1. Matthias Egger (, reader in social medicine and epidemiologya,
  2. George Davey Smith, professor of clinical epidemiologya
  1. a Department of Social Medicine, University of Bristol, Bristol BS8 2PR
  1. Correspondence to: Dr Matthias Egger


    The number of papers published on meta-analyses in medical research has increased sharply in the past 10 years (fig 1). The merits and perils of the somewhat mysterious procedure of meta-analysis, however, continue to be debated in the medical community.1 23 What, then, is meta-analysis? A useful definition was given by Huque: “A statistical analysis that combines or integrates the results of several independent clinical trials considered by the analyst to be ‘combinable.’” 4 The terminology, however, is still debated, and expressions used concurrently include “overview,” “pooling,” and “quantitative synthesis.” We believe that the term meta-analysis should be used to describe the statistical integration of separate studies, whereas “systematic review” is most appropriate for denoting any review of a body of data that uses clearly defined methods and criteria (box). Systematic reviews can include meta-analyses, appraisals of single trials, and other sources of evidence.6 In this article we examine the potentials and promise of meta-analysis of randomised controlled trials. In later articles of this series we will consider the practical steps involved in meta-analysis,7 examine various extensions beyond the calculation of a combined estimate,8 address potential biases and discuss strategies to detect and minimise the influence of these in meta-analysis of randomised trials9 and of observational studies.10 We will conclude with a discussion of unresolved issues and future developments.11 Details of relevant software will appear on the BMJ's website at the end of the series.

    Fig 1

    Number of publications about meta-analysis, 1987–96 (results from Medline search using text word and medical subject heading “meta-analysis”)

    What's in a name? The case for “meta-analysis”

    The term meta-analysis for statistically combining and analysing data from separate studies is appropriate because:

    • The term makes sense. “Meta” implies something occurring later, more comprehensive, and is often used to name a new but related discipline designated to …

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