Monotonic Aggregation of Beliefs and Tastes

Working paper
[pdf]

How should a group of agents make a decision when they face uncertainty about the consequences of possible actions? Suppose a group is indifferent between two actions and is joined by an agent who shares the group’s beliefs about the likelihood of each consequence under these actions. We show that if we give tie-breaking rights to such agents, group preferences have to be determined by assigning a weight to each of its member’s beliefs and tastes for the consequences that only depends on her own preferences.