A new method for group decision support based on ELECTRE III methodology

Group decision is usually understood as the reduction of different individual preferences on a given set to a single collective preference. At present, there are few approaches which solve the group ranking problem with multiple criteria in a widely acceptable way. Often, they rest on a poor heuristic which makes a decision about consensus ranking difficult to support. This paper presents an extension of the ELECTRE III multicriteria outranking methodology to assist a group of decision makers with different value systems to achieve a consensus on a set of possible alternatives. Our proposal starts with N individual rankings and N corresponding valued preference functions, and uses the natural heuristic provided by ELECTRE methodology for obtaining a fuzzy binary relation representing the collective preference. A comparison of this method with PROMETHEE II for group decision is carried out. We found that, in this particular application, the proposed heuristic based on majority rules combined with concessions to significant minorities, performs relatively better than a compensatory scheme based on a net flow weighted sum function.