The rise and fall of scary numbers: The effect of perceived trends on future estimates, severity ratings, and help-allocations in a cancer context

Statistical information such as death risk estimates is frequently used for illustrating the magnitude of a problem. Such mortality statistics are however easier to evaluate if presented next to an earlier estimate, as the two data points together will illustrate an upward or downward change. How are people influenced by such changes? In seven experiments, participants read mortality statistics (e.g., number of yearly deaths or expert-estimated death risks) made at two points of time about various cancer types. Each cancer type was manipulated to have either a downward trajectory (e.g., the estimated death risk was 37% in 2012, and was adjusted downward to 22% in 2014), an upward trajectory (e.g., 7% → 22%), or a flat trajectory (e.g., 22% → 22%). For each cancer type, participants estimated future mortality statistics and rated the perceived severity. They also allocated real money between projects aimed at preventing the different cancer types. Participants’ responses indicated that they thought that a trend made out of two data points would continue in the future. People also perceived cancer types with similar present mortality statistics as more severe and allocated more money to them when they had an upward trajectory compared to a flat or downward trajectory. Although there are boundary conditions, we conclude that people's severity ratings and helping behavior can be influenced by trend information even when such information is based on only two data points. (Less)