Journal
STATISTICS IN MEDICINE
Volume 28, Issue 12, Pages 1739-1751Publisher
JOHN WILEY & SONS LTD
DOI: 10.1002/sim.3582
Keywords
cluster randomized trials; sample size; binary outcomes
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Funding
- Medical Research Council [G0700837] Funding Source: researchfish
- Medical Research Council [G0700837] Funding Source: Medline
- MRC [G0700837] Funding Source: UKRI
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Cluster randomized trials (CRTs) are increasingly used to evaluate the effectiveness of health-care interventions. A key feature of CRTs is that the observations on individuals within clusters are correlated as a result of between-cluster variability. Sample size formulae exist which account for such correlations, but they make different assumptions regarding the between-cluster variability in the intervention arm of a trial, resulting in different sample size estimates. We explore the relationship for binary outcome data between two common measures of between-cluster variability: k, the coefficient of variation and rho, the intracluster correlation coefficient. We then assess how the assumptions of constant k or rho across treatment arms correspond to different assumptions about intervention effects. We assess implications for sample size estimation and present a simple solution to the problems outlined. Copyright (C) 2009 John Wiley & Sons, Ltd.
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