TABLE OF CONTENTS In the Cambridge Dictionary of Statistics in the Medical Sciences, meta-analysis is defined thus:
A collection of techniques whereby the results of two or more independent studies are statistically combined to yield an overall answer to a question of interest. The rationale behind this approach is to provide a test with more power than is provided by the separate studies themselves. The procedure has become increasingly popular in the last decade or so, but is not without its critics, particularly because of the difficulties of knowing which studies should be included and to which population final results actually apply.
In essence, meta-analysis is a more systematic approach to combining evidence from multiple research projects than the classical review article. Chalmers and Lau (1993) make the point that both approaches can be biased, but that at least the writer of a meta-analytic paper is required by the rudimentary standards of the discipline to give the data on which the conclusions are based, and to defend the development of these conclusions by giving evidence that all available data are included, or to give the reasons for not including the data. In contrast, the typical reviewer arrives at conclusions that may be biased and then selects data to back them up. Chalmers and Lau conclude, "It seems obvious that a discipline which requires that all available data be revealed and included in an analysis has an advantage over one that has traditionally not presented analyses of all the data on...
