Behavioral Science & Ethics USMLE Step 1 Practice Question

A prospective randomized controlled trial evaluates a novel laparoscopic technique for cholecystectomy compared to open surgery. The study enrolls 200 patients from a single tertiary care academic medical center located in an affluent suburban area (median household income $145,000). Inclusion criteria include age 40-65 years, BMI 18.5-29.9 kg/m², no comorbidities, adequate health literacy, and reliable follow-up capacity. The research team intentionally excluded patients with Medicaid or no insurance due to concerns about follow-up compliance. Excluded uninsured patients had mean age 58 years, BMI 31.2 kg/m², multiple comorbidities, and lived >100 miles from the hospital. After 12 months, the novel technique showed superior outcomes (shorter operative time, fewer complications, faster recovery) compared to open surgery. The findings are published and widely adopted by surgeons across the country. Which of the following most threatens the ability to generalize these results to the broader surgical population?