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Title: Deliberation, Coherent Aggregation, and Anchoring

Abstract: In this talk we will present a number of results stemming from a computational model of collective attitude formation through a combination of group deliberation and aggregation. In this model the participants repeatedly exchange and update their preferences over small sets of alternatives, until they reach a stable preference profile. When they do so the collective attitude is computed by pairwise majority voting. The model shows, on the one hand, that rational preference change can fill an existing gap in known mechanisms purported to explain how deliberation can help avoiding incoherent group preferences. On the other hand, the model also reveals that when the participants are sufficiently biased towards their own opinion, deliberation can actually create incoherent group rankings, against the received view. The model suggests furthermore that rational deliberation can exhibit high levels of path dependencies or “anchoring”, where the group opinion is strongly dependent on the order in which the participants contribute to the discussion. We will finish by discussing possible trade-offs between such positive and negative features of group deliberation.