In a case-control study, an investigator selects hospital controls from the same wards as cases. Some controls are admitted for conditions causally linked to the exposure of interest (e.g., COPD patients as controls in a lung cancer study examining smoking). This introduces:

• A Recall bias
• B Berkson's bias ✓
• C Neyman (incidence-prevalence) bias
• D Lead-time bias

Explanation

Berkson's (admission rate) bias occurs when both cases and controls are drawn from hospital patients, and the exposure of interest is associated with hospital admission in the control group, distorting the exposure prevalence. Recall bias refers to differential accuracy of recalled exposure. Neyman bias arises when cases are selected from survivors, missing fatal or rapidly resolving cases. Lead-time bias affects screening evaluation.

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

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