Multivariate Frailty Models for Exchangeable Survival Data with Covariates

We consider a multivariate lognormal frailty model for correlated exchangeable failure time data, where the marginal lifetimes have conditional Weibull distributions. We discuss Bayesian statistical methods to fit this model to experimental data with varying cluster sizes. The Bayesian inferential approach arises naturally from the hierarchical structure of the frailty model. In contrast, implementation of the maximum likelihood approach encounters practical difficulties. The methodology is illustrated with the analyses of three datasets.