A study recruits all patients attending a cardiology OPD. Controls are selected from the same OPD but have respiratory disease. The study finds an inflated OR for the association between smoking and heart disease. The specific bias operating here is:

• A Neyman's bias
• B Berkson's bias ✓
• C Hawthorne effect
• D Volunteer bias

Explanation

Berkson's bias (hospital admission rate bias) occurs when both cases and controls are selected from hospital patients. Smokers are more likely to be hospitalised for any condition, so controls from a respiratory OPD also have higher smoking rates than the general population, which paradoxically can inflate or deflate the OR depending on direction. Neyman bias relates to survivor selection in prevalent case studies. Hawthorne effect is behavioral change due to being observed. Volunteer bias affects studies dependent on self-selection.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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