Federico Valenciano

Shapley-Shubik and Banzhaf Indices Revisited

We provide a new axiomatization of the Shapley-Shubik and the Banzhaf power indices in the domain of simple superadditive games by means of transparent axioms. Only anonymity is shared with the former characterizations in the literature. The rest of the axioms are substituted by more transparent ones in terms of power in collective decision-making procedures. In particular, a clear restatement and a weaker alternative for the transfer axiom are proposed. Only one axiom differentiates the characterization of either index, and these differentiating axioms provide a new point of comparison. In a first step both indices are characterized up to a zero and a unit of scale. Then both indices are singled out by simple normalizing axioms.

Assessing success and decisiveness in voting situations

Abstract.In this paper we propose a simple model for measuring ‘success’ or ‘decisiveness’ in voting situations. For an assessment of these features two inputs are claimed to be necessary: the voting rule and the voters’ behavior. The voting rule specifies when a proposal is to be accepted or rejected depending on the resulting vote configuration. Voting behavior is summarized by a distribution of probability over the vote configurations. This basic model provides a clear common conceptual basis for reinterpreting different power indices and some related game theoretic notions coherently from a unified point of view.

Voting and collective decision-making : bargaining and power

List of figures Preface 1. Preliminaries 2. Seminal papers, seminal ambiguities 3. Take-it-or-leave-it committees 4. Bargaining committees 5. Application to the European Union Index.

The least square prenucleolus and the least square nucleolus. Two values for TU games based on the excess vector

The nucleolus and the prenucleolus are solution concepts for TU games based on the excess vector that can be associated to any payoff vector. Here we explore some solution concepts resulting from a payoff vector selection based also on the excess vector but by means of an assessment of their relative fairness different from that given by the lexicographical order. We take the departure consisting of choosing the payoff vector which minimizes the variance of the resulting excesses of the coalitions. This procedure yields two interesting solution concepts, both a prenucleolus-like and a nucleolus-like notion, depending on which set is chosen to set up the minimizing problem: the set of efficient payoff vectors or the set of inputations. These solution concepts, which, paralleling the prenucleolus and the nucleolus, we call least square prenucleolus and least square nucleolus, are easy to calculate and exhibit nice properties. Different axiomatic characterizations of the former are established, some of them by means of consistency for a reasonable reduced game concept.

SUCCESS VERSUS DECISIVENESS: CONCEPTUAL DISCUSSION AND CASE STUDY

In this article, we vindicate the relevance of the notion of success or satisfaction for the normative assessment of voting rules. We provide arguments in support of this view and emphasize the conceptual and analytical differences between this notion and that of decisiveness. The conclusions are illustrated in the case study provided by three different voting rules that have been proposed for the Council of Ministers of the European Union.

Inequality among EU citizens in the EU's Council decision procedure

Abstract This paper provides a normative assessment of the inequality among EU citizens imputable to the decision-making rule used by the European Council of Ministers. To this end, the EU decision-making process is modeled by a compound two-stage game among the EU citizens, whose respective voting power is evaluated by their Banzhaf index in the years 1958–1999. Two inequality indices measure the resulting inequality in the distribution of power among citizens. This permits us to evaluate the actual qualified majority rule and to compare this rule with an alternative rule, the so-called double majority rule.

Quaternary dichotomous voting rules

In this article, we provide a general model of “quaternary” dichotomous voting rules (QVRs), namely, voting rules for making collective dichotomous decisions (to accept or reject a proposal), based on vote profiles in which four options are available to each voter: voting (“yes”, “no”, or “abstaining”) or staying home and not turning out. The model covers most of actual real-world dichotomus rules, where quorums are often required, and some of the extensions considered in the literature. In particular, we address and solve the question of the representability of QVRs by means of weighted rules and extend the notion of “dimension” of a rule.

The bilateral consistent prekernel, the core, and NTU bankruptcy problems

It is shown that the bilateral consistent prekernel, an NTU solution concept that generalizes the Nash bargaining solution by means of a principle of bilateral consistency, is nonempty and intersects the core for a sufficiently rich class of NTU games: the class of boundary separating games, also introduced here. A second contribution of this paper is the NTU extension of the bankruptcy games introduced by Aumann and Maschler (1985). These games, which provide a new approach for dealing with bargaining problems with claims, are shown to be boundary separating, so that the results apply.

SEMIVALUES AND VOTING POWER

In this paper we revise the axiomatic foundations and meaning of semivalues as measures of power on the domain of simple games, when these are interpreted as models of voting procedures. In this context we characterize the family of preferences on roles in voting procedures they represent, and each of them in particular. To this end we first characterize the family of semivalues and each of them in particular up to the choice of a zero and a unit of scale. As a result a reinterpretation of semivalues as a class of power indices is proposed and critically discussed.

Some new results on Least Square Values for TU games

In this paper we present some new results concerning the least square family of values for TU games. We first examine the stability of these values from a dynamic point of view and propose a reinteropretation of them from the standpoint of the propernsity to disrupt approach. In the second part the family of individually rational least square (IRLS) values is introduced and an alternative kernel-like formulation of them is provided. Finally we describe a natural and simple algorithm for calculating any IRLS value of a game.