Abstract (EN)

Following Roy (1985), we will say that decision-aid consists in trying to provide answers to questions raised by actors involved in a decision process using a clearly specified model. In order to do so, the analyst often has to compare “alternatives” (see Vincke, 1989). In an approach using several criteria, the analyst aims at establishing comparisons on the basis of the evaluation of the alternatives according to several criteria. In an approach using a single criterion, the analyst seeks to build a unique criterion taking into account all the relevant aspects of the problem. In either approach, the success of decision-aid crucially depends upon the way in which the unique criterion or the family of criteria have been built. The aim of this paper is to emphasize the importance of this phase by a number of frequently encountered difficulties and some techniques to overcome them.