An investigator studies whether income is a confounder in the association between physical activity and type 2 diabetes. Which criterion must income satisfy to be classified as a confounder?

• A Income must be associated with diabetes but not with physical activity
• B Income must be the only other risk factor for diabetes in the study
• C Income must be randomly distributed between exposed and unexposed groups
• D Income must be associated with both physical activity and diabetes, and must not be an intermediate variable on the causal pathway ✓

Explanation

Three criteria define a confounder: (1) associated with the exposure (physical activity), (2) independently associated with the outcome (diabetes), and (3) not an intermediary on the causal pathway from exposure to outcome. If income caused physical activity to reduce diabetes, it would be on the causal pathway and adjustment would block a true causal mechanism.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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