Sample Size Determination for Hierarchical Longitudinal Designs with Differential Attrition Rates

• Activity Number: 310
• Type: Invited
• Date/Time: Tuesday, July 31, 2007 : 2:00 PM to 3:50 PM
• Sponsor: WNAR
• Author(s): Anindya Roy and Dulal K. Bhaumik*+ and Subhash Aryal and Robert D. Gibbons
• Companies: University of Maryland, Baltimore County and University of Illinois at Chicago and University of Illinois at Chicago and University of Illinois at Chicago
• Keywords: Cost analysis ; Dropouts ; Mixed-effects ; Power analysis ; Profile analysis ; Three-level nested design

Abstract

We consider the problem of sample size determination for three-level mixed-effects linear regression models for the analysis of clustered longitudinal data. Three-level designs are used in many areas, but in particular, multicenter randomized longitudinal clinical trials in medical or health-related research. In this case, level 1 represents measurement occasion, level 2 represents subject, and level 3 represents center. Our approach is general with respect to sampling proportions, number of groups, and attrition rates over time. In addition, we also develop a cost model, as an aid in selecting the most parsimonious of several possible competing models. We derive sample size requirements (i.e., power characteristics) for a test of treatment-by-time interaction(s) for designs based on either subject-level or cluster-level randomization.