Eliciting experts' knowledge: A comparison of two methods

This paper reports on a detailed comparison of the practical application of two well-known forecasting methods—a surprisingly rare exercise. Delphi and cross-impact analyses are among the best-known methods that apply quantitative approaches to derive forecasts from expert opinion. Despite their prominence, there is a marked shortage of clear guidance as to when and where–and how–particular methods can be useful, or as to what their costs and benefits are. This study applied the two methods to the same area, future European transport systems, using the same expert knowledge base. The results of the implementation of the two techniques were assessed and evaluated, in part through two evaluation questionnaires completed by the experts who participated in the study. This paper describes these encounters with methodology and evaluation, presents illustrative results of the forecasting study, and draws lessons as to good practice in use of these specific methods, as well as concerning methodological good practice in general—for example, stressing the need for systematic documentation, and the scope for debate about established practices.