Ultimatum and the economic logic of negotiation: the contribution of experimental economics.

Summary The theoretical analysis of negotiation amounts to reducing the variety of rules available to the different parties to reach an agreement. In this perspective, Rubinstein's (1982) model offers a resolution of a sequential, alternate-bid, finite-horizon bargaining game. By mobilizing the principle of 'backward induction', we identify a perfect subgame equilibrium in which the players reach equilibrium sharing in the first stage of the game. The ultimatum game, which assumes that the offer made is take-it-or-leave-it, is the simplest element of this model. The equilibrium sharing is then a very unequal distribution of payoffs among the players. First, the experimental study of the ultimatum game and the sequential bargaining games reveals an unparalleled preference for the equal distribution of payoffs, contrary to the predictions of the theory. The theoretical anomaly found supports the existence of reciprocal justice between negotiators assuming the existence of moral sentiments. The in-depth study of the offerer - responder relationship then highlights the multiplicity of individual motivations and the importance of <>. The plurality of moral feelings poses the problem of the internal coherence of the individual and requires their reduction. In a first approach, the reconciliation of experimental evidence and theoretical predictions amounts to incorporating non-monetary elements in the utility functions of players. Two approaches are then considered. The first one assumes that the aversion to inequality is the unifying motive of the individual's moral feelings. The second one prefers reciprocity understood as the attribution of intentions to others. The study of the relations existing between reciprocal justice and reciprocal envy is the object of an experimental protocol. In a second approach, the reduction of the individual's moral feelings is considered as the result of group interactions. Thus, reciprocal justice corresponds to the coordination of the players on a sharing assimilated to a social norm of behavior or preference. This result raises the problem of the robustness of reciprocal justice, which is then the subject of an experimental protocol.