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Confounding — USMLE Step 2 CK MCQ

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ModeratePreventive Medicine & BiostatisticsConfoundingUSMLE Step 2 CK

A 53-year-old Asian American woman comes to the clinic because of a health maintenance visit. History and focused examination are notable for observational study where coffee drinking seems linked to lung cancer because of smoking. Temperature is 98.6°F (37.0°C), blood pressure is 126/78 mmHg, pulse is 84/min, respirations are 16/min, and oxygen saturation is 98% on room air. Physical examination confirms the key finding and shows no unrelated abnormality that would better explain the presentation. The patient has no symptoms, no abnormal physical examination findings, and no previous result that would change routine evidence-based screening. Which of the following is the most likely cause of this patient's condition?

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Correct answer: B — A third variable associated with both exposure and outcome distorts the association

The vignette describes Confounding, supported by observational study where coffee drinking seems linked to lung cancer because of smoking. A third variable associated with both exposure and outcome distorts the association is the single best answer because it matches the diagnostic or management priority in this clinical setting. The other choices are plausible alternatives in related presentations, but they do not best fit the timing, findings, and guideline-directed approach described here.

Reference: https://www.ncbi.nlm.nih.gov/books/#stage-9-order-99