Characteristics of the healthy survivor effect among male and female Hanford workers

Background: The healthy survivor effect is a selection process whereby heal thy workers are selectively retained in the workforce while unhealthy worke rs are removed. Understanding this phenomenon is integral to the accurate a ssessment of exposure effects in occupational cohorts, To date, scarce info rmation has been published on the descriptive characteristics of the health y survivor effect. Methods: Follow-up mortality data on 44,154 employees from the Hanford nucl ear facility for the pel ion of 1944-1986 were used to estimate the healthy survivor effect according to frequently measured sociodemographic characte ristics. Results: While Hanford employees did not exhibit a stepwise decline in stan dardized mortality ratios according to duration of employment, workers in t he longest employment duration category demonstrated a substantial survival advantage compared to the rest of the cohort. This effect was present in b oth males and females, aid in all but the following subgroups: males hired at or after age 40, females hired before age 40, and females classified as both professional and nonprofessional. Conclusion: The findings of the present study suggest that investigators sh ould consider the potential confounding role of the healthy survivor effect when relying on SMRs or other methods, to assess the adverse health effect s of exposure in occupational cohorts. Further studies should be conducted, however to assess variation in the healthy survivor effect according to so ciodemographic characteristics. Am. J. Ind. Med. 35:343-337, 1999. (C) 1999 Wiley-Liss, Inc.