Verbal and numerical expressions of probability: It's a fifty-fifty chance

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. (C) 2000 Academic Press.