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Cluster Randomized Trial Sample Size Calculator

Pro

Calculate the sample size needed for a cluster randomized controlled trial, accounting for intra-cluster correlation.

Study Parameters
Results

Required Sample Size

280

Group 1: 140 | Group 2: 140

Achieved Power

85.0%

Effect Size

0.500

Method: Cluster RCT (Design Effect Approach)
Clusters per arm7
Total clusters14
Design effect (DEFF)1.950
ICC0.050
Cluster size20
  • •Subjects nested within clusters
  • •Intra-cluster correlation (ICC) = 0.05
  • •Average cluster size m = 20
  • •Design effect DEFF = 1.950
  • •Total clusters = 14 (7 per arm)
  • •Two-sided hypothesis test
Formula
DEFF = 1 + (m - 1) * ICC; n_adj = n_individual * DEFF; clusters = ceil(n_adj / m)
References
  1. Donner A, Klar N (2000). Design and Analysis of Cluster Randomization Trials in Health Research. Arnold.
  2. Eldridge SM, Ashby D, Kerry S (2006). Sample size for cluster randomized trials. Int J Epidemiology, 35, 1292-1300.