Issues in the meta‐analysis of cluster randomized trials

Abstract
Meta‐analyses involving the synthesis of evidence from cluster randomization trials are being increasingly reported. These analyses raise challenging methodologic issues beyond those raised by meta‐analyses which include only individually randomized trials. In this paper we review and comment on a selected number of these issues, including problems of study heterogeneity, difficulties in estimating design effects from individual trials and the choice of statistical methods. Copyright © 2002 John Wiley & Sons, Ltd.