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AbstractThis paper studies an extensive form game of coalition formation with random proposers in games with externalities. It is shown that an agreement will be reached without delay if any set of coalitions profits from merging. Even under this strong condition, the equilibrium coalition structure is not necessarily efficient. There may be multiple equilibria even in the absence of externalities, and symmetric players are not necessarily treated symmetrically in equilibrium. If the grand coalition forms without delay in equilibrium, expected payoffs must be in the core of the characteristic function game that assigns to each coalition its equilibrium payoff. Compared with the rule of order process of Ray and Vohra (Games Econ Behav 26:286–336, 1999), the bargaining procedure with random proposers tends to give a large advantage to the proposer, whereas the bargaining procedure with a rule of order tends to favor the responders. The equilibria of the two procedures cannot be ranked in general in terms of efficiency.

This paper examines the relationship between voting weights and expected equilibrium payoffs in legislative bargaining and provides a necessary and sufficient condition for payoffs to be proportional to weights. This condition has a natural interpretation in terms of the supply and demand for coalition partners. An implication of this condition is that Snyder et al.'s (2005) result, that payoffs are proportional to weights in large replicated games, does not necessarily extend to the smaller games that arise in applications. Departures from proportionality may be substantial and may arise even in well-behaved (homogeneous) games.

We examine the relationship between voting weights and expected equilibrium payoffs in legislative bargaining and provide a necessary and sufficient condition for payoffs to be proportional to weights. This condition has a natural interpretation in terms of the supply and demand for coalition partners. An implication of this condition is that Snyder et al.´s (2005) result, that payoffs are proportional to weights in large replicated games, does not necessarily extend to the smaller games that arise in applications. Departures from proportionality may be substantial and may arise even in well-behaved (homogeneous) games.

This paper analyses a model of legislative bargaining in which parties form tentative coalitions (protocoalitions) before deciding on the allocation of a resource. Protocoalitions may fail to reach an agreement, in which case they may be dissolved (breakdown) and a new protocoalition may form. We show that agreement is immediate in equilibrium, and the proposer advantage disappears as the breakdown probability goes to zero. We then turn to the special case of apex games and explore the consequences of varying the probabilities that govern the selection of formateurs and proposers. Letting the breakdown probability go to zero, most of the probabilities considered lead to the same ex post pay-off division. Ex ante expected pay-offs may follow a counterintuitive pattern: as the bargaining power of weak players within a protocoalition increases, the weak players may expect a lower pay-off ex ante.

This paper analyses a model of legislative bargaining in which parties form tentative coalitions (protocoalitions) before deciding on the allocation of a resource. Protocoalitions may fail to reach an agreement, in which case they may be dissolved (breakdown) and a new protocoalition may form. We show that agreement is immediate in equilibrium, and the proposer advantage disappears as the breakdown probability goes to zero. We then turn to the special case of apex games and explore the consequences of varying the probabilities that govern the selection of formateurs and proposers. Letting the breakdown probability go to zero, most of the probabilities considered lead to the same ex post pay-off division. Ex ante expected pay-offs may follow a counterintuitive pattern: as the bargaining power of weak players within a protocoalition increases, the weak players may expect a lower pay-off ex ante.

It is well known that proposers have an advantage in the canonical model of bargaining in legislatures: proposers are sure of being part of the coalition that forms, and, conditional on being in a coalition, a player receives more as a proposer than as a coalition partner. In this paper I show that, if parties differ in voting weight, it is possible for a party to donate part of its proposing probability to another party and be better-off as a result. This can happen even if the recipient never includes the donor in its proposals. Even though actually being the proposer is valuable, having a higher probability of being proposer may be harmful.

This paper extends the Baron-Ferejohn model of legislative bargaining to general weighted majority games with two modifications: first, payoff division can only be agreed upon after the coalition has formed (two-stage bargaining); second, negotiations in the coalition can break down, in which case a new coalition may be formed (reversible coalitions). Under the most natural bargaining protocol, both expected payoffs and actual payoff division are proportional to the voting weights provided that the set of winning coalitions of minimum weight is weakly balanced and that the breakdown probability tends to 0. Homogeneity of the voting weights is neither necessary nor sufficient for proportional payoffs. Intermediate values of the breakdown probability produce predictions consistent with the empirical evidence on portfolio allocation in Europe: a moderate propoper advantage and a linear relationship between weights and ex post payoffs for all coalition members other than the proposer.

Power indices suggest that adding new members to a voting body may increase the power of an existing member, even if the number of votes of all existing members and the decision rule remain constant. This phenomenon is known as the paradox of new members. This paper shows that the paradox has theoretically occurred in the EU using the leading model of legislative bargaining. Furthermore, it is possible for a majority of members to be in favor of enlargement, even if voters are bargaining over a fixed budget.