Biostatistics & Study Design USMLE Step 1 Practice Question
A 35-year-old woman on oral contraceptives presents with left leg swelling, pain, and warmth. Vital signs show BP 118/76, HR 92, RR 16, temp 37°C, SpO2 98%. Doppler ultrasound confirms deep venous thrombosis. Investigators analyzing contraceptive use and DVT risk find weak overall association, but stratified analysis reveals no increased risk among nonsmokers and marked increased risk among smokers. She denies smoking history. Which pattern best describes these findings?
Answer choices
- AEffect modificationCorrect answer
- BRecall bias
- CConfounding
- DAttrition bias
- EMeasurement bias
- FSelection bias
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