A cohort study measures pesticide exposure using job titles alone, and this classification is equally inaccurate for workers who later do and do not develop leukemia. The expected effect of this misclassification on the estimated exposure-disease association is:
- A It will be biased toward the null ✓
- B It will be inflated away from the null
- C It will be biased toward the alternative
- D It will be unaffected because outcome classification is accurate
Correct answer: A. It will be biased toward the null
Explanation
Non-differential misclassification of exposure, meaning errors unrelated to disease status, drives the observed measure of association toward the null value, producing an underestimate of any true effect. Differential misclassification, where accuracy differs between diseased and non-diseased subjects, can bias the estimate in either direction. Accurate outcome measurement does not protect against dilution caused by exposure misclassification.
Reference: Rothman, Greenland and Lash, Modern Epidemiology, 3rd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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