Among employees of a chemical factory, 60 deaths from respiratory cancer are observed over 10 years, whereas applying national age-specific mortality rates to the workforce gives 100 expected deaths. The standardized mortality ratio is 60. The most appropriate interpretation is:
- A The workforce appears healthier than the general population, consistent with the healthy worker effect ✓
- B The factory exposure protects against respiratory cancer
- C The expected figure was miscalculated
- D There is a 60 percent excess mortality due to occupational exposure
Correct answer: A. The workforce appears healthier than the general population, consistent with the healthy worker effect
Explanation
SMR below 100 means observed deaths are fewer than expected from general population rates. Employed populations are systematically healthier than the general population because the chronically ill and disabled are excluded from work, producing the healthy worker effect, a form of selection bias in occupational studies. It does not indicate protection by workplace exposure, nor does it imply any excess risk; option D misreads the direction of the ratio.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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