A case-control study finds an association between coffee consumption and pancreatic cancer. On review, heavy coffee drinkers in both cases and controls are predominantly smokers, and smoking is an established independent risk factor for pancreatic cancer. In this study, smoking is acting as:

• A Effect modifier
• B Selection bias
• C Intermediate variable on the causal pathway
• D Confounder ✓

Explanation

A confounder must satisfy three conditions: it is associated with the exposure, it is an independent risk factor for the outcome, and it lies outside the causal pathway between them. Smoking meets all three here, so the coffee association may partly reflect the excess of smokers among coffee drinkers. An intermediate variable would be caused by coffee itself, and an effect modifier would change the strength of the association across its levels.

Reference: Gordis Epidemiology, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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