Strategic power indices: Quarrelling in coalitions

While they use the language of game theory known measures of a priory voting power are hardly more than statistical expectations assuming voters behave randomly. Focusing on normalised indices we show that rational players would behave differently from the indices predictions and propose a model that captures such strategic behaviour.Banzhaf index, Shapley-Shubik index, a priori voting power, rational players

Strategic power indices: Quarrelling in coalitions

While they use the language of game theory known measures of a priory voting power are hardly more than statistical expectations assuming voters behave randomly. Focusing on normalised indices we show that rational players would behave differently from the in-dices predictions and propose a model that captures such strategic behaviour.Banzhaf index, Shapley-Shubik index, a priori voting power, rational players

Strategic power indices: Quarrelling in coalitions

While they use the language of game theory known measures of a priory voting power are hardly more than statistical expectations assuming the random behaviour of the players. Focusing on normalised indices we show that rational players would behave differently from the indices predictions and propose a model that captures such strategic behaviour.Economics (Jel: A)

Voting Power in the Australian Senate: 1901-2004

Indices of voting power are intended to measure the a priori degree of in.uence that a voter or party can expect to have in framing legislation or passing motions. Commonly used measures include those proposed by Shapley and Shubik (1954), Banzhaf (1965) and Deegan and Packel (1978). This paper computes these power indices for the Australian Senate for the period 1901-2004. The introduction of the Single Transferable Vote in the Senate in 1949 appears to have had a profound effect on the voting power of both major parties, as well as on the degree of concentration of voting power.

Coalition Governments in a Model of Parliamentary Democracy

We analyze the relative importance of party ideology and rents from office in the formation of coalitions in a parliamentary democracy. In equilibrium, the types of coalitions that are formed may be minimal winning, minority or surplus and they may be ideologically `disconnected'. The coalitions that form depend upon the relative importance of rents of office and seat shares of the parties. If rents are high, governments cannot be surplus. With low rents or the formateur close to the median, minority governments occur for a wider ideological dispersion. Further, there is a non-monotonic relationship between connectedness of coalitions and rents.Coalitions, Ideology, Rents

Two-Stage Bargaining with Reversible Coalitions: The Case of Apex Games

This paper studies coalition formation and payoff division in apex games under the following assumptions: 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).In contrast with the results of other two-stage models, all minimal winning coalitions may form and expected payoffs coincide with the per capita nucleolus.These results are robust to the details of the bargaining procedure.Surprisingly, having a two-stage process (rather than a one-stage process with simultaneous coalition formation and payoff division) benefits the apex player.bargaining;game theory;coalition

Voting Power in the EU Council of Ministers and Fair Decision Making in Distributive Politics

We analyze and evaluate the different decision rules describing the Council of Ministers of the EU starting from 1958 up to date. All the existing studies use the Banzhaf index (for binary voting) or the Shapley-Shubik index (for distributive politics). We argue that the nucleolus can be considered an appropriate power measure in distributive situations and an alternative to the Shapley-Shubik index. We then calculate the nucleolus and compare the results of our calculations with the conventional measures. In the second part, we analyze the power of the European citizens as measured by the nucleolus under the egalitarian criterion proposed by Felsenthal and Machover (1998), and characterize the first best situation. Based on these results we propose a methodology for the design of the optimal (fair) decision rules. We perform the optimization exercise for the earlier stages of the EU within a restricted domain of voting rules, and conclude that Germany should receive more than the other three large countries under the optimal voting rule.

Potential Maximization and Coalition Government Formation

A model of coalition government formation is presented in which inefficient, non-minimal winning coalitions may form in Nash equilibrium. Predictions for five games are presented and tested experimentally. The experimental data support potential maximization as a refinement of Nash equilibrium. In particular, the data support the prediction that non-minimal winning coalitions occur when the distance between policy positions of the parties is small relative to the value of forming the government. These conditions hold in games 1, 3, 4 and 5, where subjects played their unique potential-maximizing strategies 91, 52, 82 and 84 percent of the time, respectively. In the remaining game (Game 2) experimental data support the prediction of a minimal winning coalition. Players A and B played their unique potential-maximizing strategies 84 and 86 percent of the time, respectively, and the predicted minimal-winning government formed 92 percent of the time (all strategy choices for player C conform with potential maximization in Game 2). In Games 1, 2, 4 and 5 over 98 percent of the observed Nash equilibrium outcomes were those predicted by potential maximization. Other solution concepts including iterated elimination of dominated strategies and strong/coalition proof Nash equilibrium are also tested.Coalition formation, Potential maximization, Nash equilibrium refinements, Experimental study, Minimal winning