Ambiguity in risk assessment

•A new overall definition of ambiguity as a defining challenge to risk assessment.•Need for disentangling linguistic, contextual, and normative ambiguity.•Identification of sources and manifestations of ambiguity in risk assessment.•Basis for discussing ambiguity in an analytic-deliberative approach.•Procedure for identifying and resolving ambiguity in risk-informed decision-making.

This paper discusses and clarifies the meaning of ambiguity in risk assessment, identifies sources and manifestations of ambiguity in risk assessment, and outlines a procedure for approaching ambiguity in risk-informed decision-making. Existing definitions of ambiguity are reviewed and argued to be of limited relevance for engineering risk assessment. A new overall definition of ambiguity as a challenge to risk-informed decision-making is proposed, and linguistic, contextual, and normative ambiguity are defined as distinct categories of ambiguity. Three tables identify sources and manifestations of ambiguity in preassessment, risk analysis, and risk evaluation. The tables provide the basis for a new procedure for identifying and resolving ambiguity in an analytic-deliberative approach to risk-informed decision-making.