"My friends: it would be an error to accept": Communication and group identity in a bargaining setting

In this paper we introduce communication into intergroup ultimatum bargaining in a lab. The responder groups vote whether to accept the proposals with unanimity required either for acceptance or for rejection. In contrast with the no-communication results reported in our previous study (Elbittar, Gomberg and Sour 2011), the group decision rule does affect the individual voting behavior when subjects are allowed to exchange messages before voting. In fact, when acceptance is the default, subjects become substantially more likely to vote to reject an offer. As a result, the formal group decision-making rule turns out to have little impact on group decisions, which follow the behavior of the more confronational subjects, as predicted by the "group discontinuity hypothesis" of the psychological literature.