Effects of Group Size and Communication Availability ' On Coalition Bargaining in a Veto Game

This study examined the effects of manipulating the size of groups of male student negotiators and their ability to communicate with one another in a game in which one player held veto power (i.e., had to be included in any winning coalition). The predictions of three models, the core, the value, and the weighted probability model, were tested. The game, in which the veto player could form a winning coalition with any other single player, was repeated for'a series of 10 winning coalitions (trials). Each variable had a significant main effect on the veto players' payoffs: Payoffs' increased when group size increased, when communication opportunities were not available, and as the trials progressed. The effects for group size indicated significant differences between three-person groups and four-, five, and six-person groups, and between all of these groups and seven-person groups. The increasing payoffs . over trials were significant in the no-communication conditions, but no significant increases occurred in the conditions in which communication was available. Combined with previous results, the findings appear to be quite consistent. The increasing payoffs for the veto player when communication opportunities , were not available yielded the only support for the predictions of the core; the overall payoffs consistently supported the predictipns of the value and the weighted probability model. All of the models, however, might benefit from modifications that Incorporate the dynamic nature of coalition bargaining.