An occupational cohort of chemical plant workers shows a standardized mortality ratio of 0.85 for all-cause mortality when compared with the national population. The investigators suspect this does not reflect any protective effect of the workplace exposure. The most likely explanation is:

• A Healthy worker effect ✓
• B Berkson's bias
• C Lead time bias
• D Recall bias

Explanation

Employed populations must pass health screening at hiring and tend to be fitter than the general population, which includes the chronically ill and disabled. Comparing worker mortality with national rates therefore spuriously lowers the SMR, an artifact called the healthy worker effect. Berkson's bias arises from hospital-based sampling, and lead time bias concerns screening programs, neither of which applies to occupational cohorts.

Reference: Park's Textbook of Preventive and Social Medicine, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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