The healthy worker survivor effect and mortality at two automotive engine manufacturing plants

Attributes such as time since hire or length of followup may be important in occupational mortality due to the "healthy worker survivor effect." In a regression analysis of mortality odds ratios at two automotive engine plants, strong effects of overall employment duration (latency weighted) were observed in addition to effects for (similarly weighted) cumulative exposures. The duration effects were negative for several cancer and noncancer outcomes, and confounded exposure effects. The lung cancer odds ratio declined to 0.68 (95% CI = 0.51, 0.90) at the mean duration of employment. With control for employment duration, adjusted lung cancer odds ratios for work as millwrights increased from 3.0 to 3.8, and for work in cylinder head production, from 3.3 to 3.9. Several causes of death with strong duration effects were smoking-related, suggesting diminished smoking risk factors with increasing employment duration. Similarly, trends for cirrhosis of the liver mortality suggested the alcohol risk factor is smaller in long-duration workers. If personal risk factors are an important component of the healthy worker survivor effect, they could be powerful negative confounders of exposure-response for related outcomes. Including a term for employment duration in regression models appears to partially correct for healthy worker survivor bias.