An Evaluation of Beta-Binomial and Dirichlet-Trinomial Models for the Analysis of Reproductive and Developmental Effects

✍ Scribed by Dr. James J. Chen; Lung-An Li

• Publisher: John Wiley and Sons
• Year: 1992
• Tongue: English
• Weight: 523 KB
• Volume: 34
• Category: Article
• ISSN: 0323-3847
• DOI: 10.1002/bimj.4710340212

✦ Synopsis

The common endpoints for the evaluation of reproductive and developmental toxic effects are the number of dead/resorbed fetuses, the number of malformed fetuses, and the number of normal fetuses for each litter. The joint distribution of the three endpoints could be modelled by a Dirichlettrinomial distribution or by a product of two-beta-binomial distributions. A simulation experiment is used to investigate the biases of the maximum Likelihood estimate (MLE) for the probability of adverse effects under the Dirichlet-trinomial model and the beta-binomial model. Also, the type I errors and powers of the likelihood ratio test for comparing the difference between treatment and control are evaluated for the two underlying models.

In estimation, the two MLE's are comparable, the bias estimates are small. In testing, the likelihood ratio test is generally more powerful under the Dirichlet-trinomial model than the beta-binomial model. The type 1 error rate is greater than the nominal level using the Dirichlettrinomial model in some cases, when the data are generated from the two-beta-binomial model, and it is less than the nominal level using the beta-binomial model in other cases. when the data are generated from the Dirichlet-trinomial model.