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Activity Number: 433
Type: Contributed
Date/Time: Wednesday, August 5, 2009 : 8:30 AM to 10:20 AM
Sponsor: ENAR
Abstract - #303750
Title: Power and Sample Size Estimation for the Clustered Wilcoxon Test
Author(s): Bernard Rosner*+ and Robert J. Glynn
Companies: Channing Laboratory and Brigham and Women's Hospital
Address: Harvard Medical School, Boston, MA, 02115,
Keywords: rank sum test ; ophthalmology ; clustered data
Abstract:

An assumption of the Wilcoxon rank sum test is independence of sampling units both within and between groups which will be violated in the clustered data setting such as in ophthalmological studies. Therefore, we have proposed the clustered Wilcoxon test to account for clustering among multiple subunits within the same cluster (Rosner, Glynn and Lee, Biometrics 2003, 2006). However, power estimation is needed for studies that use this analytic approach. We have recently published methods for estimating power and sample size for the ordinary Wilcoxon rank sum test (epub ahead of print, Biometrics, 2008). In this paper we present extensions of this approach to estimate power for the clustered Wilcoxon test. These methods are applied to data from the Sorbinil Retinopathy Trial to help plan future studies of diabetic retinopathy.

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