Verbal probabilities: An alternative approach

Abstract

Previous studies of verbal probabilities have tried to place expressions like a chance, possible, and certain on 0–1 numerical probability scales. We ask instead, out of a range of outcomes, which outcome a verbal probability suggests. When, for instance, a sample of laptop batteries lasts from 1.5 to 3.5 hours, what is a certain and what is a possible duration? Experiment 1 showed that speakers associate certain with low values and possible with (unlikely) high or maximal values. In Experiment 2, this methodology was applied to several positive and negative verbal probability phrases, showing a preference for high rather than low or middle values in a distribution. Experiment 3 showed that such maxima are not universally described by large numbers. For instance, maximum speed is often described in terms of a small number of time units. What can (possibly) happen is accordingly sometimes described with very low and sometimes with very high values, depending upon focus of interest. Finally, participants in Experiment 4 were given the role of hearers rather than speakers and were asked to infer outcome ranges from verbal probabilities. Hearers appeared to be partly aware of speakers' tendencies to describe outcomes at the top of the range.

Keywords:

• Verbal probabilities
• Communication
• Framing
• Range estimates
• Judgements

This research was supported by an Aurora Grant for French–Norwegian research exchange and an internal grant from the Department of Psychology to the first author.

Notes

¹ Because the data did not meet the multivariate normality assumption we conducted an additional series of one-tailed Mann–Whitney tests, comparing the median scores of the lower bound, upper bound, and range midpoints as function of the probability phrase. All comparisons were statistically significant at p < .002, except the midpoint comparison of flats, although the minimum and maximum bounds of the range differed significantly, even in this case.

²In a pretest designed for the studies reported by Juanchich, Teigen, and Gourdon (in press), participants were asked to estimate the probabilities that speakers would have in mind when saying “It is possible [certain] that the laptop battery will last 3 hours” (along with seven other verbal expressions). In this context, which comes close to the vignettes used in the present experiments, possible was given a mean probability value of 52.6%, and certain received a mean score of 92.1%.