A case-control study investigating pesticide exposure and non-Hodgkin lymphoma enrolls cases from a cancer registry and controls from the same hospital's orthopaedic ward. The main validity concern regarding this design is:

• A Information bias due to differential recall between cases and controls
• B Berkson's bias from selecting controls who may over-represent pesticide users ✓
• C Neyman bias from excluding incident cases who died before enrolment
• D Length-biased sampling due to the cancer registry source

Explanation

Berkson's bias (hospital admission rate bias) arises when cases and controls are both drawn from hospital populations; orthopaedic patients may be farmers with higher occupational pesticide exposure, inflating the apparent association. Differential recall (option A) is a genuine concern in case-control studies but is not the primary structural flaw here — the control selection is. Neyman bias affects prevalence-based studies. Length-biased sampling relates to screening trials.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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