title: Ignorance is not probability.
abstract: The distinction between ignorance about a parameter and knowing only a probability distribution for that parameter is of fundamental importance in risk assessment. Brief dialogs between a hypothetical decisionmaker and a risk assessor illustrate this point, showing that the distinction has real consequences. These dialogs are followed by a short exposition that places risk analysis in a decision-theoretic framework, describes the important elements of that framework, and uses these to shed light on Terje Aven's criticism of nonprobabilistic purely "objective" methods. Suggestions are offered concerning a more effective approach to evaluating those methods.
authors.affiliation: Quantitative Decisions, 1235 Wendover Road, Rosemont, PA 19010, USA. whuber@quantdec.com
authors.forename: William A
authors.initials: WA
authors.lastname: Huber
mesh_terms: D006801:Humans; D011336:Probability; D012306:Risk; D018570:Risk Assessment