Verbal uncertainty expressions: Literature review

Abstract This paper summarizes findings of a literature review on verbal uncertainty expres- sions. There have been several studies in this field in the last twenty years. The main motivation behind these studies is that using verbal expressions is preferred by humans in certain situations and may be practically applied in decision making. It is postulated to reflect better non-numerical nature of the data, avoid the misleading impression of precision by being implicitly vague, and be easier for people to deal with. Two major findings of this research are that people are internally consistent in their use of these expressions and that there is a great between-subject variability. The probabilistic meaning of the phrases is also shown to be highly context sensitive, with an asymmetry and a large overlap between different phrases. Variability of verbal expressions is severly underestimated by people using them and verbal communication poses the danger of considerable misunderstandings. On the other hand, there exist phrases that most of the people agree upon and a careful choice of a small vocabulary is able to facilitate precise communication. Appendix gives a list of all verbal uncertainty phrases encountered in the literature. Introduction The concept of subjective probability, mapping of person's belief onto the real number between 0 (event believed to be impossible) and 1 (event believed to occur with certainty), plays a major role in any modern theory of decision making. However, on various grounds, people often resist expressing their opinions numerically, preferring instead to use non- numerical terms, like probable, chances are, almost certain, etc