Mixed-effects modelling of Kevlar fibre failure times through Bayesian non-parametrics

We examine the accelerated failure time model for univariate data with right censoring, with application to failure times of Kevlar fibres grouped by spool, subject to different stress levels. We propose a semi-parametric modelling by letting the error distribution be a shape-scale mixture of Weibull densities, the mixing measure being a normalised generalised gamma measure. We obtain posterior estimates of the regression parameter and also of credibility intervals for the predictive distributions and their quantiles, by including the posterior distribution of the random mixing probability in the MCMC scheme. The number of components in the non-parametric mixture can be interpreted as the number of groups, having a prior distribution induced by the non-parametric model, and is inferred from the data. Compared to previous results, we obtain narrower interval estimates of the quantiles of the predictive survival function. Other diagnostic plots, such as predictive tail probabilities and Bayesian residuals, show a good agreement between the model and the data.