Retrospective studies and failure time models

The proportional hazards failure time model of Cox (1972) is adapted to the retrospective epidemiological study, in which cases and controls are sampled from a population in order to relate disease incidence rates to exposure to suspected risk factors. The method permits simultaneous study of several exposure variables, that may be discrete or continuous or a mixture of both, in the presence of additional explanatory variables and competing risks. The proportional hazards framework provides a fresh look at the concepts of matching, choice of controls, confounding and effect modification.