A TAXONOMY OF ISSUES RELATED TO THE USE OF EXPERT JUDGMENTS IN PROBABILISTIC SAFETY STUDIES

Expert judgments are frequently used in probabilistic safety assessments (PSA). However, the methods employed in practice are very crude and a large gap exists between the theoretical methods available and actual practice. A taxonomy of issues related to the use of expert judgments in PSA was considered necessary to identify the needs of the practitioners and the applicability of existing models. In this paper, a taxonomy of issues related to the use of expert judgments in PSA is systematically reviewed with examples from case studies. Issues surrounding the expert judgment process can be classified into two categories-(a) elicitation, and (b) the use of expert judgments. Various elements of these categories, such as model and parameter uncertainty, decomposition, the use of multiple experts, the selection of experts, expert training, elicitation, effect of information provided to experts, expert calibration, availability of evidence, opinion aggregation and dependence are then discussed. The issues of expert bias. calibration and dependence are of special concern. Sources of expert bias and dependence are discussed with some thoughts on overcoming them using examples from selected case studies.