Meta-analyses of cluster randomization trials. Power considerations.

A commonly cited purpose for conducting a meta-analysis of randomized trials is to increase the statistical power for detecting the effect of an intervention on a specified set of endpoints. At the same time, it also has been noted by several authors that many large-scale cluster randomization trials have not had the power to detect small or even moderate effect sizes. The loss of efficiency associated with cluster randomization relative to individual randomization, and the frequent failure of investigators to take this loss of efficiency into account at the planning stage of a trial, undoubtedly contributes to this problem. In this article, the authors present an approach that may be used to estimate the power of a planned meta-analysis that includes trials that are cluster randomized. Two examples are presented.