Patients' interpretation of qualitative probability statements

BACKGROUND: Physicians often use qualitative probability statements to compare treatment options or describe risks of treatment, especially if exact numerical information is not readily available. OBJECTIVES: To determine (1) the effect of context, experience, age, gender, race, occupation, and education on patients' numerical interpretation of probability terms and (2) patient preferences for information about side effects (qualitative or numerical). DESIGN: Cross-sectional survey. SETTING: A university-based family practice in Ann Arbor, Mich. PARTICIPANTS: Patients 18 years of age and older and parents of patients younger than 18 years of age seen during January and February 1993 for any reason except complete physical examination. METHODS: A questionnaire presented scenarios of minor and major complications related to four different medical conditions. Participants were asked to estimate how many people of 100 would have a complication if their physician described the risk for the complication in each scenario as unlikely. Participants were then asked whether they preferred receiving information from their physician about the risk for complications in words or numbers. RESULTS: Of 345 questionnaires distributed, 307 patients (89%) completed them. The rates assigned to the minor complications were significantly higher than the rates assigned to the major complications (P = .0001). Participants who had experienced the described complication reported significantly higher rates for the minor complications of vaccination and surgery (P = .0001 and P = .0235, respectively). Education had a significant effect only on the rates assigned to vaccination complications (P = .0069). Occupation had a significant effect only on the rates assigned to antibiotic side effects (P = .0090). CONCLUSIONS: When a physician uses qualitative probability statements, he or she must be sensitive to the patient's previous experience with that procedure or medication. Also, if one wants to convey the same potential rate of occurrence for major and minor side effects, then one needs to use different words for each.