A cohort study of pesticide factory employees finds total mortality significantly LOWER than that of the general population, despite known toxic exposures. An epidemiologist warns this finding may be spurious. The most appropriate explanation is:
- A Neyman's bias, since prevalent rather than incident cases were studied
- B Healthy worker effect, since employed populations are selected for better baseline health than the general population ✓
- C Ecological fallacy, since group-level data were applied to individuals
- D Information bias, since exposure was misclassified
Correct answer: B. Healthy worker effect, since employed populations are selected for better baseline health than the general population
Explanation
The healthy worker effect is a form of selection bias in occupational cohorts: employment itself requires a minimum level of health, so workers have lower background mortality than the whole population, which includes the chronically ill and unemployed. Comparisons should ideally use an internal reference group or another workforce. Neyman's bias concerns survival into prevalence studies, ecological fallacy concerns aggregation of data, and information bias concerns misclassification rather than this mortality deficit.
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.