Robustness of a semi-parametric proportional intensity model

The Prentice, Williams, Peterson (PWP) semiparametric model for the failure processes of repairable systems involves regression on explanatory variables across strata defined by the failure-event count. A heuristic method is developed for assessing the robustness of the PWP model, where the true underlying process is nonhomogeneous Poisson with power-law intensity function. The PWP model performed well for large samples and increasing rates of occurrence of failures and poorly for small samples and decreasing rates of occurrence of failures.>