Judgment change during Delphi-like procedures: The role of majority influence, expertise, and confidence

This study investigates individual opinion change and judgmental accuracy in Delphi-like groups. Results reveal that the accuracy of judgmental probability forecasts increases over Delphi rounds (in terms of proportion correct and appropriateness of confidence) when statistical summaries or written rationales are provided from other members of an individual's nominal group, but does not increase in a control iteration condition (without feedback). Additionally, subjects who gave more appropriate probability forecasts on the first round exhibited least opinion change, although measures of confidence were unrelated to opinion change. Results also show that majority opinion exerts strong opinion pull on minority opinion even when the majority favours an incorrect answer (irrespective of the nature of feedback provided). The implications of these results for the utility and conduct of the Delphi technique are discussed, in particular, with respect to selecting panellists and choosing an appropriate feedback format.