Because collective decision processes are central to the management function of most organizations, it is important to understand them better and to improve them if possible. One common view of group decision processes is that they should offer participants the opportunity to confront and resolve the differences in their points of view. New cognitive and technical tools may help to facilitate the sharing of individuals’ reasoning and preferences, but only if they do not require participants to reveal information that they wish to keep private, perhaps for strategic or personal reasons. The aim of this study is to test experimentally one such approach, contained in the Group Decision Support System, GRUS, which allows decision makers to use a multi-criteria approach to problem structuring that can involve both public (shared) and private criteria.