Sample Size Determination for Testing Equality in a Cluster Randomized Trial with Noncompliance

Abstract

For administrative convenience or cost efficiency, we may often employ a cluster randomized trial (CRT), in which randomized units are clusters of patients rather than individual patients. Furthermore, because of ethical reasons or patient's decision, it is not uncommon to encounter data in which there are patients not complying with their assigned treatments. Thus, the development of a sample size calculation procedure for a CRT with noncompliance is important and useful in practice. Under the exclusion restriction model, we have developed an asymptotic test procedure using a tanh⁻¹(x) transformation for testing equality between two treatments among compliers for a CRT with noncompliance. We have further derived a sample size formula accounting for both noncompliance and the intraclass correlation for a desired power 1 − β at a nominal α level. We have employed Monte Carlo simulation to evaluate the finite-sample performance of the proposed test procedure with respect to type I error and the accuracy of the derived sample size calculation formula with respect to power in a variety of situations. Finally, we use the data taken from a CRT studying vitamin A supplementation to reduce mortality among preschool children to illustrate the use of sample size calculation proposed here.

Key Words:

• Cluster sampling
• Dirichlet multinomial model
• Intraclass correlation
• Noncompliance
• Power
• Sample size calculation
• Type I error

ACKNOWLEDGMENT

The authors thank the two referees for many valuable and useful suggestions to improve the clarity and contents of this article.

Notes

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