How probable is probable? A numerical translation of verbal probability expressions

• Published in: Journal of forecasting 1982-07, Vol.1 (3), p.257-269
• Main Author: Beyth-Marom, Ruth
• Format: Article
• Language: English
• Subjects: Forecast/Forecasts/Forecasting; Forecasting; Probability estimation; Probability/Probabilities; Subjective probability; Verbal probability
• ISSN: 0277-6693; 1099-131X
• DOI: 10.1002/for.3980010305

The reported experiment took place in a professional forecasting organization accustomed to giving verbal probability assessments (‘likely’, ‘probable’, etc.). It attempts to highlight the communication problems caused by verbal probability expressions and to offer possible solutions that are compatible with the forecasters overall perspective on their jobs Experts in the organization were first asked to give a numerical translation to 30 different verbal probability expressions most of which were taken from the organization's own published political forecasts. In a second part of the experiment the experts were given 15 paragraphs selected from the organization's political publications each of which contained at least one verbal expression of probability. Subjects were again asked to give a numerical translation to each verbal probability expression The results indicate that (a) there is a high variability in the interpretation of verbal probability expressions and (b) the variability is even higher in context. Possible reasons for the context effect are discussed and practical implications are suggested.