Sample size calculations for the design of cluster randomized trials: A summary of methodology.

Journal Article (Journal Article)

Cluster randomized trial designs are growing in popularity in, for example, cardiovascular medicine research and other clinical areas and parallel statistical developments concerned with the design and analysis of these trials have been stimulated. Nevertheless, reviews suggest that design issues associated with cluster randomized trials are often poorly appreciated and there remain inadequacies in, for example, describing how the trial size is determined and the associated results are presented. In this paper, our aim is to provide pragmatic guidance for researchers on the methods of calculating sample sizes. We focus attention on designs with the primary purpose of comparing two interventions with respect to continuous, binary, ordered categorical, incidence rate and time-to-event outcome variables. Issues of aggregate and non-aggregate cluster trials, adjustment for variation in cluster size and the effect size are detailed. The problem of establishing the anticipated magnitude of between- and within-cluster variation to enable planning values of the intra-cluster correlation coefficient and the coefficient of variation are also described. Illustrative examples of calculations of trial sizes for each endpoint type are included.

Full Text

Duke Authors

Cited Authors

  • Gao, F; Earnest, A; Matchar, DB; Campbell, MJ; Machin, D

Published Date

  • May 2015

Published In

Volume / Issue

  • 42 /

Start / End Page

  • 41 - 50

PubMed ID

  • 25766887

Electronic International Standard Serial Number (EISSN)

  • 1559-2030

Digital Object Identifier (DOI)

  • 10.1016/j.cct.2015.02.011


  • eng

Conference Location

  • United States