Sample size estimation in cluster randomized studies with varying cluster size

Amita K. Manatunga, Michael G. Hudgens, Shande Chen

Research output: Contribution to journalArticlepeer-review

77 Scopus citations


Cluster randomized studies are common in community trials. The standard method for estimating sample size for cluster randomized studies assumes a common cluster size. However often in cluster randomized studies, size of the clusters vary. In this paper, we derive sample size estimation for continuous outcomes for cluster randomized studies while accounting for the variability due to cluster size. It is shown that the proposed formula for estimating total cluster size can be obtained by adding a correction term to the traditional formula which uses the average cluster size. Application of these results to the design of a health promotion educational intervention study is discussed.

Original languageEnglish
Pages (from-to)75-86
Number of pages12
JournalBiometrical Journal
Issue number1
StatePublished - 1 Dec 2001


  • Cluster randomized
  • Longitudinal data
  • Sample size
  • Varying cluster size


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