Proceedings of the Section on Epidemiology of the American Statistical Association
The survival distributions of the service life times of respirator safety devices produced by different manufacturers are determined using frailty models to account for unobserved differences in manufacturing processes and raw materials. The gamma and positive stable frailty distributions are used to obtain survival distribution estimates when the baseline hazard is assumed to be Weibull. Frailty distributions are compared using laboratory test data of the failure times for 104 respirator cartridges produced by 10 different manufacturers. Likelihood ratio tests results indicated that both frailty models provide a significant improvement over a Weibull independence model.