Collective Choices Under Ambiguity

We investigate experimentally whether collective choice environments matter for individual attitudes to ambiguity. In a simple two-urn Ellsberg experiment, one urn offers a 45 % chance of winning a fixed monetary prize while the other offers an ambiguous chance. Participants choose either individually or in groups of three. Group decision rules vary in the level of individual responsibility for the others’ payoffs: the collective choice is taken by majority, randomly delegated to two group members, or randomly delegated to a single group member. Although most participants display consistent ambiguity attitudes across their decisions, taking responsibility for the others tends to foster ambiguity aversion.