A study comparing mortality of factory employees with the general population finds employees have lower death rates than expected. This apparent protective effect arises because severely ill individuals are screened out at recruitment into employment. This phenomenon is an example of:
- A Information bias
- B Confounding
- C Selection bias ✓
- D Ecological fallacy
Correct answer: C. Selection bias
Explanation
The healthy worker effect occurs because workers must be reasonably fit to obtain and retain employment, so occupational cohorts appear healthier than the general population, which includes the unemployed, chronically ill and institutionalized. It is a form of selection bias because the comparison group differs systematically in baseline health. Confounding requires a third variable associated with both exposure and outcome, which is not the mechanism here.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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