Who is Trusted for a Second Opinion? Comparing Collective Advice from a Medical AI and Physicians in Biopsy Decisions After Mammography Screening

Artificial Intelligence (AI) is increasingly integrated into clinical practice, but its influence on patient decision-making, particularly when AI and physicians disagree, remains unclear. To examine collective advice, we investigated a breast cancer screening scenario using (1) a qualitative interview study (N=9) and (2) a quantitative experiment (N=339) where participants received either consistent or conflicting biopsy recommendations. Qualitative findings include the need for empathetic care, the importance of patient autonomy, and a desire for a four-eyes principle. Quantitative findings accordingly show that patients generally trust physicians more than AI but still tend to follow AI recommendations due to risk aversion. When both advised a biopsy, 99% adhered; if both advised against it, 25% still proceeded. In conflicting scenarios, 97% followed the physician's advice, whereas 66% followed the AI if it recommended the biopsy. These results underscore the need for careful interaction design of collective healthcare advice to prevent unnecessary healthcare procedures.