Models of the healthy worker effect in industrial cohorts.

The patterns of standardized mortality ratios (SMRs) with duration of follow-up and duration of service which are characteristic of the healthy worker effect in occupational cohort studies have been simulated using models of selection and survivor effects. The models support current theories about the population dynamics which underlie the selection effect but highlight inadequacies in our understanding of the survivor effect. Several possible models were tested and methods of generating appropriate data are discussed. It is important that the healthy worker effect should be better understood as it can present so large a problem in the interpretation of occupational risk estimates.