Cluster trials in implementation research: estimation of intracluster correlation coefficients and sample size

The cluster randomized trial with a concurrent economic evaluation is consi dered the gold standard evaluative design for the conduct of implementation research evaluating different strategies to promote the transfer of resear ch findings into clinical practice. This has implications for the planning of such studies, as information is needed on the effects of clustering on b oth effectiveness and efficiency outcomes. This paper describes the design considerations specific to implementation research studies, focusing partic ularly on the estimation of sample size requirements and on the need for re liable information on intracluster correlation coefficients for both effect iveness and efficiency outcomes. Copyright (C) 2001 John Wiley & Sons, Ltd.