Risk Communication: Absolute versus Relative Expressions of Low-Probability Risks

Abstract

According to most prescriptive decision rules, formally equivalent methods of communicating risk information should have identical effects on risk-taking behavior, even if the pertinent displays are different. The present work takes two methods commonly employed in epidemiology, incidence rates and relative risks, and examines their comparative effects on risk-avoidant behavior. In Experiment 1, we presented 108 undergraduates with information about risks associated with different brands of tires and toothpaste and displayed that information either as incidence rates or as a relative risk ratio. For the tires product, subjects given the relative risk format were willing to pay more money for a safer product than were subjects given the incidence rate format. There were, however, no differences between the two conditions for the toothpaste product. Experiment 2 evaluated two potential explanations for the difference in findings between the two products. The majority of the data supported an "editing" hypothesis, which suggests that extreme low-probability risks, such as those associated with tire blowouts, are edited to "essentially nil risk," while more moderate risks, such as those associated with periodontal disease, are considered to be small but significant. These findings are discussed in the context of fuzzy trace theory and related models, which suggest that people reason on the basis of simplified representations rather than on the literal information available.