A case-control study is conducted to examine the association between dietary fat intake and colorectal cancer. Cases are recruited from hospital oncology wards, while controls are patients admitted for non-gastrointestinal, non-cancer conditions. The odds ratio (OR) for high fat intake among cases vs controls is 1.8 (95% CI: 1.2–2.7). The investigators note that dietary recall over the past year is likely influenced by awareness of cancer diagnosis. Which specific bias best explains this distortion?

• A Berkson's bias
• B Neyman's bias
• C Ecologic fallacy
• D Rumination bias (recall bias) ✓

Explanation

Rumination (recall) bias occurs when cases, aware of their diagnosis, recollect past exposures more thoroughly or differently than controls, inflating the apparent exposure-disease association. Berkson's bias is a hospital admission rate bias affecting both cases and controls from hospital populations. Neyman's (incidence-prevalence) bias occurs when severe or rapidly fatal cases are missed because the study captures only survivors. Ecologic fallacy arises when group-level data are wrongly applied to individuals.

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.