‘Expert information’ versus ‘expert opinions’. Another approach to the problem of eliciting/ combining/using expert knowledge in PRA

In the traditional approach to eliciting expert knowledge for use in risk assessment and decision analysis, the expert is asked for his opinion about, say, the numerical value of some unknown parameter λ. This opinion is then expressed as a point estimate, λ_i, or a probabilistic estimate, P_i(λ). Much attention and debate is then given, in the traditional approach, to methods of weighing and combining the opinions from the individual experts.The present paper advocates another approach in which we ask each expert, instead, for his body of evidence, E_i, relevant to the value of λ. In this way, the approach first arrives at a consensual body of evidence, E − {E_i}, and second, at a consensual curve p(λ|E) that expresses our knowledge about λ based on that body of evidence.The essential difference between this ‘expert information’ approach and the traditional ‘expert opinion’ approaches may be captured in the slogan: lsWeigh evidence, not experts!’