Characteristics of the healthy worker effect: A comparison of male and female occupational cohorts

The healthy worker effect (HWE) poses a serious methodological problem to investigators of occupational cohorts in that it may masks mortality excesses that result from occupational exposures. This problem is further complicated by the fact that the strength of the HWE generally varies according to sociodemographic, employment, and time-related factors. While the HWE has been well documented among numerous cohorts of male workers, little is known about its expression among female occupational workers. Follow-up mortality data on 44,154 employees from the Hanford nuclear facility for the period of 1944-1986 were examined using standardized mortality ratio (SMR) analysis to assess whether modifiers of the HWE were expressed differently in females than in males. Results of this analysis show that while the HWE was modified by race, age at hire, occupational class, and length of follow-up in both male and female cohorts, different patterns of modification emerged across the two subgroups. Learning about how gender differentiates expression of the HWE will help investigators more precisely assess the confounding effect of the HWE in studies of working cohorts. Therefore, this study's findings are relevant for designing and interpreting future occupational cohort studies.