doi 10.1287/inte.1080.0397 ©2008 INFORMS When Is Uncertainty About Uncertainty

In areas of risk assessment ranging from terrorism to health, safety, and the environment, authoritative guidance urges risk analysts to quantify and display their uncertainties about inputs that significantly affect the results of an analysis, including their uncertainties about subjective probabilities of events. Such “uncertainty characteri-zation ” is said to be an important part of fully and honestly informing decision makers about the estimates and uncertainties in analyses that support policy recommendations, enabling them to make better decisions. But is it? Characterization of uncertainties about probabilities often carries zero value of information and accomplishes nothing to improve risk-management decisions. Uncertainties about consequence probabilities are not worth characterizing when final actions must be taken based on information available now. “But there seemed to be no chance of this, so she began looking at everything about her to pass away the time.” Lewis Carroll, Alice in Wonderland Key words: risk analysis; decision analysis; uncertainty analysis; expert elicitation; probability; uncertainty characterization. History: This paper was refereed. Quantitative risk analysts are blessed today witha wealth of advice and instruction designed t