In a case-control study of bladder cancer and artificial sweetener exposure, cases are recruited from urology clinics while controls are recruited from orthopaedics clinics in the same hospital. Sweetener use happens to be higher among orthopaedic patients than in the general population. This leads to:
- A Overestimation of the odds ratio due to Berkson's bias
- B Underestimation of the odds ratio due to Berkson's bias ✓
- C Recall bias favouring the null hypothesis
- D Neyman bias leading to survivor selection
Explanation
Berkson's bias (hospital admission rate bias) occurs when both cases and controls are selected from hospitals, and hospitalization rates differ between exposure groups. If orthopaedic controls have unusually high sweetener exposure compared with the general population, the control group artificially inflates exposure prevalence, making the odds ratio appear smaller than the true population value — a form of underestimation. Recall bias affects case-control studies through differential recall but is not the mechanism here; Neyman bias involves selection of survivors in prevalent-case designs.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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Written and medically reviewed by the StethoPrep medical team.