Imagine that you have just received a colon cancer diagnosis and need to choose between two different surgical treatments. One surgery, the "complicated surgery," has a lower mortality rate (16% vs. 20%) but compared to the other surgery, the "uncomplicated surgery," also carries an additional 1% risk of each of four serious complications: colostomy, chronic diarrhea, wound infection, or an intermittent bowel obstruction. The complicated surgery dominates the uncomplicated surgery as long as life with complications is preferred over death.
In our first survey, 51% of a sample (recruited from the cafeteria of a university medical center) selected the dominated alternative, the uncomplicated surgery, justifying this choice by saying that the death risks for the two surgeries were essentially the same and that the uncomplicated surgery avoided the risk of complications. In follow-up surveys, preference for the uncomplicated surgery remained relatively consistent (39%-51%) despite (a) presenting the risks in frequencies rather than percents, (b) grouping the 4 complications into a single category, or (c) giving the uncomplicated surgery a small chance of complications as well. Even when a pre-decision "focusing exercise" required people to state directly their preferences between life with each complication versus death, 49% still chose the uncomplicated surgery.
People’s fear of complications leads them to ignore important differences between treatments. This tendency appears remarkably resistant to debiasing approaches and likely leads patients to make healthcare decisions that are inconsistent with their own preferences.