A researcher investigates whether low birth weight causes childhood asthma. She enrolls children with asthma (cases) and without asthma (controls) and then asks mothers to recall their child's birth weight. Cases' mothers are more likely to over-report problems at birth. This best describes:

• A Observer bias
• B Recall bias ✓
• C Lead-time bias
• D Length-time bias

Explanation

Recall bias occurs when cases and controls recall past exposures differently due to disease awareness — cases are more motivated to search for a cause and may misremember or overreport prior exposures. This is a classic limitation of retrospective case-control studies. Observer bias involves the investigator systematically measuring differently in case vs. control groups. Lead-time and length-time biases relate to screening programmes, not recall of exposures.

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.