What is the Ratio Bias?
Ratio Bias is a cognitive bias that affects people’s perception of probabilities when comparing different ratios. It occurs when individuals perceive the likelihood of an event to be higher or lower based on the absolute difference between the numbers involved in the ratio, rather than the actual proportional difference. This bias can lead to incorrect evaluations of risk, affecting decisionmaking processes in various domains, such as finance, healthcare, and gambling. Ratio bias is a reflection of individuals’ limited ability to accurately assess probabilities and showcases the influence of cognitive shortcuts and heuristics on human judgment and decisionmaking.
Examples of the Ratio Bias

Lottery Tickets
In a lottery game, people may perceive the odds of winning as better if they buy more tickets, even if the increase in odds is negligible. For example, a person may feel more confident about winning when they have 10 tickets out of 1000, compared to having 1 ticket out of 100, even though the odds of winning are nearly the same (1% vs. 0.1%).

Healthcare Decisions
Patients may be more likely to opt for a medical treatment if the success rate is presented as 99 out of 100 (99%) compared to 198 out of 200 (also 99%). The absolute difference in the numerator (1 vs. 2) creates an illusion of a more significant difference in success rate, even though the proportional difference remains the same.
Shortcomings and Criticisms of the Ratio Bias

Impact on Decisionmaking
Ratio bias can lead to suboptimal decisionmaking, as individuals may overestimate or underestimate the probabilities of various outcomes. This can result in unnecessary risktaking or overly cautious behavior, with potentially negative consequences in personal, professional, and financial domains.

Limited Generalizability
Research on ratio bias has predominantly used laboratory experiments and hypothetical scenarios, which may not always translate to realworld decisionmaking contexts. Further research is needed to understand the extent to which ratio bias influences reallife choices and judgments.

Individual Differences
Not all individuals are equally susceptible to ratio bias. Factors such as cognitive abilities, numeracy skills, and decisionmaking styles can influence the likelihood of falling prey to this cognitive bias. Recognizing these individual differences is crucial for developing tailored interventions to mitigate the effects of ratio bias.