In a case-control study of oral cancer, cases were asked about their past consumption of tobacco and alcohol. The investigator found that cases reported much higher exposure than controls, but part of this difference occurred because patients with cancer had thought deeply about their habits after diagnosis while controls had not. This type of error is best described as:

• A Interviewer bias
• B Confounding
• C Selection bias
• D Recall bias ✓

Explanation

Recall bias occurs when cases, being aware of their disease status, search their memory more thoroughly and report exposures differently from controls, leading to differential misclassification. Interviewer bias would require the data collector to probe or record differently between groups, which is not described here. Selection bias arises at recruitment, and confounding involves a third variable distorting both exposure and outcome, none of which fits this scenario.

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

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Written and medically reviewed by the StethoPrep medical team.