Behavioral Science & Ethics USMLE Step 1 Practice Question
A prospective cohort study evaluates a novel minimally invasive technique for total knee arthroplasty. The primary outcome is functional improvement at 12 months postoperatively, measured by the Knee Injury and Osteoarthritis Outcome Score (KOOS). Of 200 patients enrolled, the published results report a 92% success rate based on 184 patients who completed the full 12-month follow-up. Chart review reveals that 16 patients were excluded from the final analysis: 10 experienced early surgical site infections requiring revision, 4 developed severe stiffness requiring manipulation under anesthesia, and 2 were lost to follow-up. The authors justified this approach by stating that 'only patients with adequate follow-up data and without protocol violations could be meaningfully evaluated.' A peer reviewer notes that inclusion of all 200 enrolled patients with intention-to-treat analysis would substantially lower the reported success rate. Which type of bias most accurately describes this methodological flaw?
Answer choices
- AHawthorne effect, wherein knowledge of being studied causes patients to modify their postoperative rehabilitation behavior
- BPublication bias, wherein journals preferentially accept studies with positive outcomes for dissemination
- CAttrition bias, wherein differential loss of participants during follow-up, particularly those with adverse outcomes, systematically inflates the estimated treatment effectCorrect answer
- DRecall bias, wherein patients with worse functional outcomes have difficulty accurately remembering their baseline symptom severity
- ESelection bias, wherein the initial enrollment process fails to create comparable groups at study inception
- FDetection bias, wherein outcome assessors are not blinded to treatment assignment, leading to differential outcome ascertainment
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