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BMC Medical Research Methodology
Published in: BMC Medical Research Methodology 1/2005

Open Access 01-12-2005 | Research article

A priori postulated and real power in cluster randomized trials: mind the gap

Authors: Lydia Guittet, Bruno Giraudeau, Philippe Ravaud

Published in: BMC Medical Research Methodology | Issue 1/2005

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Abstract

Background

Cluster randomization design is increasingly used for the evaluation of health-care, screening or educational interventions. The intraclass correlation coefficient (ICC) defines the clustering effect and be specified during planning. The aim of this work is to study the influence of the ICC on power in cluster randomized trials.

Methods

Power contour graphs were drawn to illustrate the loss in power induced by an underestimation of the ICC when planning trials. We also derived the maximum achievable power given a specified ICC.

Results

The magnitude of the ICC can have a major impact on power, and with low numbers of clusters, 80% power may not be achievable.

Conclusion

Underestimating the ICC during planning cluster randomized trials can lead to a seriously underpowered trial. Publication of a priori postulated and a posteriori estimated ICCs is necessary for a more objective reading: negative trial results may be the consequence of a loss of power due to a mis-specification of the ICC.
Appendix
Available only for authorised users
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Metadata
Title
A priori postulated and real power in cluster randomized trials: mind the gap
Authors
Lydia Guittet
Bruno Giraudeau
Philippe Ravaud
Publication date
01-12-2005
Publisher
BioMed Central
Published in
BMC Medical Research Methodology / Issue 1/2005
Electronic ISSN: 1471-2288
DOI
https://doi.org/10.1186/1471-2288-5-25

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