An occupational cohort study follows factory workers exposed to benzene for 15 years and compares cancer incidence with the general population. The Standardised Mortality Ratio (SMR) is found to be 0.72. This MOST likely reflects:

• A A true protective effect of benzene exposure
• B Underreporting of deaths in the factory cohort
• C Inadequate follow-up duration to detect cancer mortality
• D The Healthy Worker Effect — employed workers are healthier than the general population at baseline ✓

Explanation

An SMR < 1.0 (here 0.72 means 28% fewer deaths than expected) in an occupational cohort compared to the general population is classic evidence of the Healthy Worker Effect: employed individuals are healthier at baseline (must be fit to work) compared to the general population which includes the chronically ill and unemployed. This systematic bias can mask occupational hazards and is a form of selection bias inherent to occupational cohort studies.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.