This paper contrasts four methods for obtaining forecasting from a group of experts: (1) statistical average of the individual forecasts, (2) face-to-face discussion to reach consensus, (3) Delphi, and (4) Estimate-Talk-Estimate (E-T-E). A review of the literature, along with a reanalysis of an important E-T-E study, provided little grounds to suggest one method to be more accurate than another. Fischer then used the four methods to aggregate opinions on a simple problem, estimating grade point averages of 10 randomly selected students given sex, high school GPA, and SAT scores. The four aggregation methods procured estimates of comparable accuracy. Fischer concluded that in terms of accuracy “it makes little or no difference how one aggregated conflicting opinions of experts.” He suggested cost and acceptability are likely to be relevant criteria. These methods differ on cost (#1 being the least expensive) and on acceptability by the group (#2 offering the highest). Fischer omitted mention of Dalkey (1969) who found that method 1 (averaging) was slightly superior to group discussion for simple problems, and of Hall, Mouton and Blake (1963) who found method 2 (consensus) was superior to unstructured discussion in making predictions in what may have been a more complex case. My conclusion from theses studies is that structured group process is superior to unstructured group process, but that a variety of structured approaches yield similar accuracy. Hopefully we shall hear more on this subject.
Dalkey, Norman C. (1969), "Analyses from a group opinion study," Futures, 1, 541-551.
Hall, Ernest, J., Mouton, J. S. and Blake, R. R..(1963), "Group problem-solving effectiveness under conditions of pooling vs. interaction," Journal of Social Psychology, 59, 147-157.