Vaccine skepticism reflects basic cognitive differences in mortality-related event frequency estimation.

Vaccines have prevented and nearly eliminated several deadly diseases, yet they face skepticism from the public. One potential driver of vaccine skepticism is how people process event frequencies such as rare adverse reactions to vaccines. Misestimations may distort the perceived risks of vaccinating. The current study examined how vaccine skepticism is related to accuracy in event frequency processing. In Experiment 1, participants (n = 158) estimated the frequencies of several vital statistics (e.g., 'How many people die per year in the U.S. from emphysema?'). Higher levels of vaccine skepticism were associated with lower accuracy in frequency estimation and over-estimation of rare events. In Experiment 2 (n = 109), we again found that vaccine skepticism was negatively associated with vital statistic estimation accuracy but not for emotionally neutral or positive events. These results suggest that vaccine skepticism may arise from basic individual differences in processing events associated with mortality or negative affect.