A study compares mortality of employees of a large steel plant with the general population of the same region and finds significantly LOWER all-cause mortality among the workers. The best explanation is:

• A Occupational exposure to steel dust protects against chronic disease
• B Information bias arising from misclassification of causes of death
• C Workers under-report deaths to retain employment benefits
• D Employed persons are healthier than the general population, which includes those too ill to work ✓

Explanation

This is the healthy worker effect, a form of selection bias. People who gain and keep employment are systematically healthier than the total population, which includes the chronically ill, disabled and institutionalised who cannot work. Comparing workers with the general population therefore spuriously lowers their apparent mortality. The correct approaches are an internal comparison group of less exposed workers or comparison against an appropriately selected standard population.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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