A case-control study examining the association between dietary fat intake and pancreatic cancer recruits hospital patients with recently diagnosed pancreatic cancer and matches them with orthopaedic surgery patients. The controls are more likely than the general population to have low-fat diets because orthopaedic patients are advised to reduce weight before surgery. This constitutes which type of bias?

• A Neyman bias
• B Protopathic bias
• C Rumination bias
• D Berkson's bias ✓

Explanation

Berkson's bias (hospital admission bias) arises when both cases and controls are selected from a hospital population, leading to a distorted relationship because hospital patients have different exposure profiles than the general population. Here the orthopaedic controls have systematically low-fat diets unrelated to pancreatic cancer, biasing the OR away from the null. Neyman (incidence-prevalence) bias affects studies where rapidly fatal cases are missed. Protopathic bias occurs when the outcome precedes exposure. Rumination bias is recall bias linked to cases dwelling on past 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.