Epidemiology & Prevention USMLE Step 1 Practice Question
A 32-year-old female presents with left leg swelling and pain. She uses oral contraceptives and smokes one pack daily. Vital signs: BP 118/76, HR 92, RR 16, Temp 37°C, SpO2 98%. D-dimer is elevated at 850 ng/mL; venous ultrasound confirms deep venous thrombosis. Investigators note weak overall association between oral contraceptive use and DVT, but find no increased risk among nonsmokers and marked increased risk among smokers. She denies recent surgery. Which best describes this epidemiologic pattern?
Answer choices
- AEffect modificationCorrect answer
- BMeasurement bias
- CAttrition bias
- DConfounding
- ERecall bias
- FSelection bias
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