Important decisions are often determined by group vote. Institutional provisions may stipulate who has the authority to determine the group's agenda. According to cooperative game theory, this privilege gives the leader a great deal of power to control the outcome. In a series of experiments, the authors demonstrate the influence of norms on coalitions and decisions. Subjects were assigned to groups with two agenda setters, two issues, and concentric indifference curves. Three theories were tested: coalitional rationality, group fairness, and coalitional integrity. The pattern of coalition formation, coalition dissolution, and decisions was consistent only with coalitional integrity. The integrity norm (members will not join a coalition requiring them to vote against the interests of prior coalition members) generates friction in coalition dynamics. Clearly, when formulating an agenda, leaders must consider a potential partner's coalitional history. Theories of group decision making must be sensitive to social constraints as well as self-interest.
