A case-control study examining the association between pesticide exposure and non-Hodgkin lymphoma enrolls patients from a tertiary oncology centre and selects controls from the same hospital's orthopaedic wards. Both cases and controls are asked to recall pesticide exposure over the preceding 10 years. Which bias MOST threatens the internal validity of this study?
- A Berkson's bias ✓
- B Recall bias
- C Neyman (prevalence-incidence) bias
- D Protopathic bias
Explanation
Using hospital orthopaedic controls when cases come from the same oncology centre creates Berkson's (admission rate) bias because hospitalized controls have their own set of illnesses and exposures not representative of the source population, distorting the exposure-disease relationship. Recall bias, though also present, is secondary here; Berkson's is the dominant structural flaw arising from control selection. Neyman bias applies when prevalent rather than incident cases are enrolled. Protopathic bias occurs when treatment for an early symptom is mistaken for exposure.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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