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Re‐estimating sample size in cluster randomised trials with active recruitment within clusters
Author(s) -
Schie S.,
Moerbeek M.
Publication year - 2014
Publication title -
statistics in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.996
H-Index - 183
eISSN - 1097-0258
pISSN - 0277-6715
DOI - 10.1002/sim.6172
Subject(s) - sample size determination , cluster (spacecraft) , statistics , range (aeronautics) , sample (material) , variance (accounting) , cluster size , cluster randomised controlled trial , statistical power , computer science , type i and type ii errors , mathematics , medicine , randomized controlled trial , physics , materials science , accounting , electronic structure , surgery , quantum mechanics , business , composite material , thermodynamics , programming language
Often only a limited number of clusters can be obtained in cluster randomised trials, although many potential participants can be recruited within each cluster. Thus, active recruitment is feasible within the clusters. To obtain an efficient sample size in a cluster randomised trial, the cluster level and individual level variance should be known before the study starts, but this is often not the case. We suggest using an internal pilot study design to address this problem of unknown variances. A pilot can be useful to re‐estimate the variances and re‐calculate the sample size during the trial. Using simulated data, it is shown that an initially low or high power can be adjusted using an internal pilot with the type I error rate remaining within an acceptable range. The intracluster correlation coefficient can be re‐estimated with more precision, which has a positive effect on the sample size. We conclude that an internal pilot study design may be used if active recruitment is feasible within a limited number of clusters. Copyright © 2014 John Wiley & Sons, Ltd.