The logic and role of meta-analysis in clinical research.

The term meta-analysis refers to the quantitative combination of data from independent trials. Where the result of such combination is a descriptive summary of the weight of the available evidence, the exercise is of undoubted value. Attempts to apply inferential methods, however, are subject to considerable methodological and logical difficulties. The selection and quality of the trials included, population bias, and the specification of the population to which inference may properly be made are problems to which no satisfactory solutions have been proposed. Insightful quantitative description ought not to differ materially from inferential conclusions; where discrepancies exist the inferential techniques should be regarded with extreme caution.