Understanding meta-analyses

Meta-analysis, a quantitative approach to integrating empirical research findings involving numerous statistical techniques and unique methodological issues, was developed to improve reviewing practices. To assess whether meta-analyses meet the rigorous scientific standards formulated, consumers need special information. Most publications on the subject concern the complex methodological and statistical issues, having been written mainly for potential conductors of meta-analyses. Thus, the needs of the potential consumers have largely been neglected. To fill this gap readers are given a general introduction to the aims and problems of meta-analyses, detailed enough to understand the critical issues. Recommendations for evaluating meta-analyses are formulated. A critical analysis of 48 meta-analyses shows that the high standards demanded by the meta-analysts have yet to be attained. Suggestions on how to improve their quality and practical relevance are summarized both to show consumers what they can at best expect from a meta-analysis and to encourage conductors to use more of these to improve their work.