Abstract #302144

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JSM 2003 Abstract #302144
Activity Number: 470
Type: Contributed
Date/Time: Thursday, August 7, 2003 : 10:30 AM to 12:20 PM
Sponsor: Biometrics Section
Abstract - #302144
Title: Estimates, Power and Sample Size Calculations for Two-Sample Ordinal Outcomes under Before-After Study Designs
Author(s): Pamela A. Ohman Strickland*+ and Shou-En Lu
Companies: UMDNJ and University of Medicine and Dentistry of New Jersey
Address: Division of Biometrics, Suite 2200, New Brunswick, NJ, 08903-2688,
Keywords: matched data ; conditional modeling ; estimating equations ; logistic regression
Abstract:

Sample size calculations are given for comparing two groups of subjects on an ordinal outcome in experiments where the subjects are measured before and after intervention. These calculations apply to log-odds models with random intercepts, treatment, time, and treatment-by-time interaction terms, the latter being the term of interest. The assumed forms of the odds ratios are flexible, allowing for proportional odds, adjacent categories, or other conditional models for ordinal responses. Simulation studies show that, for given sample sizes, the nominal and actual powers of the proposed test are similar.

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