Verbal uncertainty expressions: A critical review of two decades of research

The frequency with which verbal uncertainty expressions are employed suggests that they play an important role in the communication of states of uncertainty and may have an important role in emerging technologies such as Expert Systems. This article critically reviews empirical studies of verbal uncertainty expressions spanning two decades of research between 1967 and 1987 with the principal conclusions that: (1) People are highly internally consistent in their use of verbal uncertainty expressions; (2) No conclusions about between-subject variability are justified principally because (a) there is currently no consensus as to what is to count as consistent or inconsistent use and (b) there are several factors that confound purported analyses of between-subject consistency such as the composition of the stimulus set and the scaling tasks themselves; (3) One study suggests that assessments of the meaning of verbal uncertainty expressions may be conditioned by the prior perceived probabilities of the events they describe. However, other interpretations of this study are open. The review also discusses the more general epistemological question of whether the concept of uncertainty as manifest by verbal uncertainty expressions is really amenable to the unidimensional framework within which empirical studies have been conceived. I am indebted to Dylan Jones (UWIST) for his encouragement and support and to John Fox, (ICRF), Tom Wallsten and David Budescu for comments on earlier drafts. This work was supported, in part, by the Science and Engineering Research Council while the author was a postgraduate student at the Department of Applied Psychology, UWIST (now UWCC School of Psychology).