Abstract #300334

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JSM 2003 Abstract #300334
Activity Number: 94
Type: Contributed
Date/Time: Monday, August 4, 2003 : 8:30 AM to 10:20 AM
Sponsor: Biometrics Section
Abstract - #300334
Title: The Presence of Extra-Binomial Variation and Exact Conditional Tests of the Binomial Distribution
Author(s): Ji-Hyun Lee*+ and Bahjat F. Qaqish
Companies: University of North Carolina and University of North Carolina, Chapel Hill
Address: 1000 Smith Level Rd. #N5, Carrboro, NC, 27510-2515,
Keywords: overdispersion ; binary responses ; exact conditional test ; exact p values ; score tests
Abstract:

In toxicological experiments, the number of experimental units is often small. Exact methods for testing and estimation of treatment effects in logistic regression models are available. However, the validity of these methods relies on the binomial assumption. Litter effects in toxicological experiments lead to overdispersion, making the binomial assumption untenable. Although several tests of that assumption are available, those tests rely on large-sample theory which may not provide a good approximation in smaller samples. An exact test of the binomial assumption is developed in this paper. The exact approach is based on the multiplicative binomial model proposed by Altham (1978). Data from several toxicity studies illustrate our method.

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