A study comparing mortality of factory employees with the general population finds that workers have substantially lower death rates from all causes. Before concluding that employment protects health, the epidemiologist should recognize that this comparison is distorted by:
- A Recall bias
- B Lead time bias
- C Healthy worker effect, a form of selection bias ✓
- D Publication bias
Correct answer: C. Healthy worker effect, a form of selection bias
Explanation
Workers must be reasonably fit to obtain and retain employment, so any occupational cohort starts healthier than the general population, which includes the chronically ill, disabled and unemployed. This healthy worker effect is a classic selection bias in occupational studies and produces spuriously low mortality in the employed group. The correct comparator is a similar workforce without the specific exposure under study. Recall bias distorts reported past exposure, lead time bias affects screening outcomes, and publication bias affects meta-analyses.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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