Risk communication formats for low probability events: an exploratory study of patient preferences

Clear communication about the possible outcomes of proposed medical interventions is an integral part of medical care. Despite its importance, there have been few studies comparing different formats for presenting probabilistic information to patients, especially when small probabilities are involved. The purpose of this study was to explore the potential usefulness of several new small-risk graphic communication formats.

Information about the likelihoods of cancer and cancer prevention associated with two hypothetical cancer screening programs were used to create an augmented bar chart, an augmented grouped icon display, a flow chart, and three paired combinations of these formats. In the study scenario, the baseline risk of cancer was 53 per 1,000 (5.3%). The risk associated with cancer screening option A was 38 per 1,000 (3.8%) and the risk associated with screening option B was 29 per 1,000 (2.9%). Both the augmented bar chart and the augmented grouped icon display contained magnified views of the differences in cancer risk and cancer prevention associated with the screening programs. A convenience sample of 29 subjects (mean age 56.4 years; 76% men) used the Analytic Hierarchy Process (AHP) to indicate their relative preferences for the six formats using 15 sequential paired comparisons.

The most preferred format was the combined augmented bar chart + flow diagram (mean preference score 0.43) followed by the combined augmented icon + augmented bar chart format (mean preference score 0.22). The overall differences among the six formats were statistically significant: Kruskal-Wallis Chi Square = 141.4, p < 0.0001. The three combined formats all had statistically significant higher preferences scores than the single format displays (p < 0.05).

These findings suggest that patients may prefer combined, rather than single, graphic risk presentation formats and that augmented bar charts and icon displays may be useful for conveying comparative information about small risks to clinical decision makers. Further research to confirm and extend these findings is warranted.