Curbing the COVID-19 pandemic remains an ongoing global challenge. Institutionsoften release information about confirmed COVID-19 cases by citing the totalnumber of cases (e.g., 100,000), their (relative) frequency (e.g., 100 per1,000,000), or occasionally their proportion (e.g., 0.0001) in a region. Icompared the effect of these three presentation formats — total cases,frequency, and proportion — on people’s perceived risk. I foundpeople perceived a higher risk of COVID-19 from a total-cases format than fromfrequency formats when the denominators are relatively small, and the lowestrisk from a proportion format. Correspondingly, people underestimated totalinfections when given frequency and overestimated frequency when given totalnumber of cases. Additional comparisons were made among mathematicallyequivalent variations of frequency formats (e.g., 1 in 100, 10 in 1,000, 1,000in 10,000, etc.). The results provided qualified support for denominatorneglect, which seems to occur in bins into which denominators are grouped (e.g.,1–1000, 10000–100000), such that only across bins couldparticipants perceive differences. Finally, a mixed format of proportion andtotal cases reduced perceived risks from total cases alone, while a mixed formatof frequency and total cases failed to produce similar results. I conclude byproviding concrete suggestions regarding COVID-19 information releases.

Most decision-making models describing individual differences in heuristics and biases tasks build on the assumption that reasoners produce a first incorrect answer in a quick, automatic way which they may or may not override later and that the advantage of high capacity reasoners arises from this late correction mechanism. To investigate this assumption, we developed a mouse-tracking analysis technique to capture individuals’ first answers and subsequent thinking dynamics. Across two denominator neglect task experiments, we observed that individuals initially move the mouse cursor towards the correct answer option in a substantial number of cases suggesting that reasoners may not always produce an incorrect answer first. Furthermore, we observed that, compared to low capacity reasoners, high capacity individuals revise their first answer more frequently if it is incorrect and make fewer changes if it is correct. However, we did not find evidence that high capacity individuals produce correct initial answers more frequently. Consistent with the predictions of previous decision-making models, these results suggest that in the denominator neglect task the capacity-normativity relationship arises after the initial response is formulated. The present work demonstrates how the analysis of mouse trajectories can be utilized to investigate individual differences in decision-making and help us better apprehend the dynamics of thinking behind decision biases.

Proportion responding (PR) is the preference for proportionally higher gains, such that the same absolute quantity is valued more as the reference group decreases. This research investigated this kind of proportion PR in decisions about saving lives (e.g., saving 10/10 lives is preferred to saving 10/100 lives). The results of two studies suggest that PR does not stem from an overall tendency to choose higher proportions, but rather from faulty deliberative reasoning. In particular, people who display PR are less likely to engage in deliberative reflection as measured by response time, the Process Dissociation Procedure, the Cognitive Reflection Test, a numeracy test, and a task assessing denominator neglect. This association between faulty deliberation and PR was observed only when choosing the highest proportion was non-normative because it came at the expense of absolute gains (e.g., saving 10/10 lives is preferred to saving 11/100 lives). These results help to make sense of discrepant findings in previous research, pertaining to how PR relates to biased reasoning and decision making.