In a research study, it is found that people who smoke tobacco cigarettes drink more...

A confounder is a variable associated with both the exposure and the outcome but not in the causal pathway. In this study, coffee drinking is associated with smoking (the actual risk factor for lung cancer), but not independently associated with lung cancer.

Toronto Notes 2023 – Epidemiology Chapter:

“A confounder is a third variable that distorts the observed association between an exposure and an outcome. It must be associated with both the exposure and the outcome, but not a result of the exposure.”

MCCQE1 Objectives (Population Health > 97-3: Study Design and Bias):

“Recognize and control for confounding in the interpretation of observational study data.”

Coffee is not a risk factor (B) since it’s not independently associated with lung cancer, and it's not selection bias (C), which involves how participants are enrolled in a study.

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