Document Detail

Calculating sample sizes for cluster randomized trials: We can keep it simple and efficient!
MedLine Citation:
PMID:  23017638     Owner:  NLM     Status:  In-Data-Review    
OBJECTIVE: Simple guidelines for calculating efficient sample sizes in cluster randomized trials with unknown intraclass correlation (ICC) and varying cluster sizes.
METHODS: A simple equation is given for the optimal number of clusters and sample size per cluster. Here, optimal means maximizing power for a given budget or minimizing total cost for a given power. The problems of cluster size variation and specification of the ICC of the outcome are solved in a simple yet efficient way.
RESULTS: The optimal number of clusters goes up, and the optimal sample size per cluster goes down as the ICC goes up or as the cluster-to-person cost ratio goes down. The available budget, desired power, and effect size only affect the number of clusters and not the sample size per cluster, which is between 7 and 70 for a wide range of cost ratios and ICCs. Power loss because of cluster size variation is compensated by sampling 10% more clusters. The optimal design for the ICC halfway the range of realistic ICC values is a good choice for the first stage of a two-stage design. The second stage is needed only if the first stage shows the ICC to be higher than assumed.
CONCLUSION: Efficient sample sizes for cluster randomized trials are easily computed, provided the cost per cluster and cost per person are specified.
Gerard J P van Breukelen; Math J J M Candel
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Journal of clinical epidemiology     Volume:  65     ISSN:  1878-5921     ISO Abbreviation:  J Clin Epidemiol     Publication Date:  2012 Nov 
Date Detail:
Created Date:  2012-09-28     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  8801383     Medline TA:  J Clin Epidemiol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  1212-8     Citation Subset:  IM    
Copyright Information:
Copyright © 2012 Elsevier Inc. All rights reserved.
Department of Methodology and Statistics, CAPHRI School for Public Health and Primary Care, Maastricht University, PO Box 616, 6200 MD Maastricht, The Netherlands. Electronic address:
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