Background: Because most medical decisions must be made when there is uncertainty about the outcome, a good understanding of how likely the possible outcomes are is crucial for good medical decision making. The best format for presenting probabilistic information to patients, however, is unknown. Current data support: a) the use of dot diagrams, flow charts, and bar charts and b) the use of multiple presentation formats. The goal of this study was to compare patient preferences for these 3 presentation formats used singly and in combination.

Population: A convenience sample of 29 patients who volunteered to participate in a study of medical decision making.

Methods: Comparative data about the likelihoods of preventing cancer associated with 2 hypothetical cancer screening programs were used to create a bar chart, a flow chart, and a “1,000 faces” dot diagram and 3 paired combination formats. The patients used the Analytic Hierarchy Process (AHP) to compare the 6 formats and derive a quantitative scale that sums to 1 that indicates their strength of preference for each.

Results: The mean age of the patient sample was 55 years; 76% were men. The highest ranked presentation format was the combined bar chart and flow diagram (mean preference 0.43), followed by the combined dot diagram and bar chart (mean preference 0.22), the combined dot diagram and flow diagram (mean preference 0.15), and the three single format options (mean preferences 0.10, 0.07, and 0.04). The overall differences among the 6 formats were statistically significant: Kruskal-Wallis Chi Square = 141.4, p < 0.00001. The 3 combined formats were all significantly different from all other options by the Bonferroni pairwise comparison test.

Conclusion: These results suggest that probabilistic data for use in medical decision making should be presented to patients in multiple formats. Of the 3 combined formats tested, patients strongly preferred bar charts + flow diagrams to combined formats that included “1,000 face” dot diagrams.