An occupational cohort of chemical plant workers is found to have lower all-cause mortality than the general population, despite documented exposure to several hazardous agents. The most likely explanation for this paradoxical finding is:

• A Cohort effect reflecting generational differences in mortality
• B Recall bias in the documentation of occupational exposures
• C Healthy worker effect, a form of selection bias, because employed persons are healthier than the general population ✓
• D Lead time bias from earlier detection of disease in workers

Explanation

Workers must pass health screening and maintain sufficient fitness to hold employment, so any workforce is systematically healthier than the general population, which includes the chronically ill and disabled. Comparing worker mortality against general population rates therefore biases results toward lower mortality, masking occupational hazards. The correct comparator is another working population with comparable selection. This is a classic selection bias specific to occupational cohort studies, not a cohort effect or information bias.

Reference: Gordis Epidemiology, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.