Problems induced by meta-analyses.

Over 150 meta-analyses of randomized control trials have so far been published in the English language, and new ones are appearing at a rate of over fifteen per year. This explosion of a relatively new method of evaluating clinical medicine presents a number of challenges to statisticians and those responsible for health care policy. The pitfalls of retrospective research must be avoided, and the quality of the original trials should be evaluated. Heterogeneity of the control event rates and the treatment differences need to be dealt with statistically. Most important are the problems raised by the need to update meta-analyses as new trials are published.