In a cohort study evaluating the association between smoking and coronary artery disease, the crude relative risk is 3.0. After stratification by hypertension status, the RR in hypertensives is 3.1 and in non-hypertensives is 2.9. The Mantel-Haenszel pooled RR is 3.0. This finding is best described as:

• A Positive confounding by hypertension
• B Negative confounding by hypertension
• C Effect modification by hypertension
• D No confounding and no effect modification ✓

Explanation

When the stratum-specific estimates (3.1 and 2.9) are similar to each other and to the crude estimate (3.0), and the pooled estimate equals the crude, there is neither confounding nor effect modification by the stratification variable. Confounding would produce a notable difference between crude and adjusted estimates; effect modification would produce markedly different stratum-specific estimates.

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

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