A case-control study on bladder cancer and artificial sweetener use yields an OR of 1.8. After stratifying by gender, the OR in males is 1.7 and in females is 1.9, both close to the crude OR. This finding suggests:

• A Effect modification by gender
• B Gender is a confounder of the association
• C Positive confounding has inflated the crude OR
• D Gender is neither a confounder nor an effect modifier ✓

Explanation

Confounding is present when the stratum-specific estimates differ substantially from the crude estimate; effect modification (interaction) is present when stratum-specific estimates differ substantially from each other. Here, both stratum-specific ORs (1.7 and 1.9) are close to the crude OR (1.8) and close to each other, indicating gender is neither a confounder nor an effect modifier.

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

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