Work has progressed in developing nonparametric Bayes methods for analysis of multivariate data from toxicology studies. These methods allow one to assess how the profile of health responses over time changes as the level of exposure to a potentially adverse chemical changes. In order to allow individual animals vary in their tendency to have an adverse response, such as the development of a tumor, a common modeling strategy is to include a latent fraily variable. Our contribution is to allow this frailty to vary flexibly over time as the animal ages. This frailty trajectory can be considered as a low dimensional summary of the changes that occur with age in gene expression and the occurrence of mutations in key genes. We applied this framework to data from cancer chemopreventive experiments investigating the effects of antioxidants in fruit and vegetables.
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