title: Verbal and Numerical Expressions of Probability: "It's a Fifty-Fifty Chance"
abstract: When estimating risks, people may use "50" as an expression of the verbal phrase "fifty-fifty chance," without intending the associated number of 50%. The result is an excess of 50s in the response distribution. The present study examined factors determining the magnitude of such a "50 blip," using a large sample of adolescents and adults. We found that phrasing probability questions in a distributional format (asking about risks as a percentage in a population) rather than in a singular format (asking about risks to an individual) reduced the use of "50." Less numerate respondents, children, and less educated adults were more likely to say "50." Finally, events that evoked feelings of less perceived control led to more 50s. The results are discussed in terms of what they reveal about how people express epistemic uncertainty. Copyright 2000 Academic Press.
authors.affiliation: Department of Social and Decision Sciences, Carnegie Mellon University, Eindhoven, The Netherlands
authors.lastname: de Bruin WB
authors.initials: B
authors.lastname: Fischhoff
authors.initials: SG
authors.lastname: Millstein
authors.initials: BL
authors.lastname: Halpern-Felsher