In this paper we report the results of an e-democracy experiment in which a group of supporters of a large political party were asked to debate online about ways to reform the electoral law. We compared a traditional online forum with an online platform that can be used to build a collective argument map capturing the various proposals and their associated pros and cons. The aim of the study is to assess the capability of this representation-centric tool to support online collective deliberation in a real world case, as compared to a traditional online discussion. By comparing users' experience across several metrics related to usability, activity levels, and quality of collaboration our findings show the online forum produced more activity and ideas and its users perceived a better quality of the collaboration process, while the argumentation tool helped to reduce the amount of self-referential arguments and encourage viewing and rating of others' posts.
