Berkson's bias is a systematic error specific to hospital-based case-control studies. It arises because:

• A Cases are more likely to remember past exposures than controls
• B Hospital admission rates differ between exposed and unexposed, and between diseased and healthy ✓
• C Controls selected from hospitals have a higher prevalence of the study disease
• D Loss to follow-up is higher in the exposed group

Explanation

Berkson's bias (hospital admission rate bias) occurs in hospital-based case-control studies when the combination of the exposure and the disease each independently increases the probability of hospital admission. If both cases and controls are drawn from hospital patients, controls may be over-represented among individuals with the exposure because hospitalized patients are not representative of the community. This distorts the exposure-disease association. Option A describes recall bias; option C is incorrect because controls from hospital are non-cases; option D describes attrition bias.

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

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