Frequency or total number? A comparison of different presentation formats on risk perception during COVID-19

Curbing the COVID-19 pandemic remains an ongoing global challenge. Institutions often release information about confirmed COVID-19 cases by citing the total number of cases (e.g., 100,000), their (relative) frequency (e.g., 100 per 1,000,000), or occasionally their proportion (e.g., 0.0001) in a region. I compared the effect of these three presentation formats — total cases, frequency, and proportion — on people’s perceived risk. I found people perceived a higher risk of COVID-19 from a total-cases format than from frequency formats when the denominators are relatively small, and the lowest risk from a proportion format. Correspondingly, people underestimated total infections when given frequency and overestimated frequency when given total number of cases. Additional comparisons were made among mathematically equivalent variations of frequency formats (e.g., 1 in 100, 10 in 1,000, 1,000 in 10,000, etc.). The results provided qualified support for denominator neglect, which seems to occur in bins into which denominators are grouped (e.g., 1–1000, 10000–100000), such that only across bins could participants perceive differences. Finally, a mixed format of proportion and total cases reduced perceived risks from total cases alone, while a mixed format of frequency and total cases failed to produce similar results. I conclude by providing concrete suggestions regarding COVID-19 information releases.