An investigator studying the incidence of diabetes in a cohort notices that participants who are healthier and more compliant with follow-up have better outcomes compared to those who drop out. Over time, only the healthiest remain in the cohort. This is best described as:
- A Healthy worker effect
- B Hawthorne effect
- C Attrition bias (differential loss to follow-up) ✓
- D Information bias
Explanation
When participants who remain in a study differ systematically from those who drop out (e.g., dropouts are sicker, less compliant, or more exposed), this creates attrition bias — a form of selection bias that distorts the estimated incidence and associations. As healthier participants selectively remain, estimated outcome rates may be artificially lowered. The healthy worker effect is a specific selection bias in occupational cohort studies where employed workers are inherently healthier than the general population. Hawthorne effect is behavioural change due to observation.
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.