A proportional hazards modeling of multisample reliability data
The Weibull distribution, the most commonly used reliability model, accomodates only certain increasing only certain increasing and decreasing hazard functions, but nonmonotone, especially bathtub, shaped hazard functions are often encountered in reliability studies. The generalized Weibull family introduced in Mudholkar and Kollia (1994) contains distributions with unimodal, bathtub shaped, and a broader variety of monotone hazard functions. Moreover, it is closed under proportional hazards meodeling, which is desirable, interesting and convenient in studies involving multiple samples occurring in repair-reuse type reliability situations. The analysis of multisample data is illustrated using the bus motor failure mileages first studied by Davis(l952).