Assessing success and decisiveness in voting situations

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.The authors would like to thank to M. Braham, M. Machover, N. Megiddo and F. Steffen, for their comments, and to J. F. Mertens for pointing out a misstatement, in all cases referring to previous versions of this paper. This research has been supported by the DGES of the Spanish Ministerio de Educación y Cultura under project PB96-0247, by the Spanish Ministerio de Ciencia y Tecnología under project BEC2000-0875, and by the Universidad del País Vasco under project UPV/EHU00031.321-HA-7918/2000. The first author also acknowledges the financial support from a postdoctoral grant from the Basque Government (2000–2001) and the Spanish Ministerio de Ciencia y Tecnología under the Ramón y Cajal Program.     

Strategy-proof voting schemes with continuous preferences

We prove that all nondictatorial voting schemes whose range has more than two alternatives will be manipulable, when their domain is restricted to the set of all continuous preferences over alternatives. Our result neither implies nor is implied by the original Gibbard-Satterthwaite theorem, except if the number of alternatives is finite, when they coincide. A new, direct line of reasoning is used in the proof. It is presented in an introductory section, which may be useful in classroom situations.The work of S. Barberà is partially supported by Research Grant PB 86-0613, from the Dirección General de la Investigación Científica y Técnica, Spanish Ministry of Education.     

Extending an order to the power set: The Leximax Criterion

This work analyzes the issue of ranking the levels of well-being enjoyed by an agent when dealing with her opportunity set in a freedom of choice context. We try to propose a natural extension of a preference relation over a (possibly) infinite set X to its power set, compatible with the finite Leximax criterion. This research has been supported by Comisión Interministerial de Ciencia y Tecnología, SEC2000-0838 (Ballester), and Dirección General de Enseñanza Superior e Investigación Científica, PB98-0551 (De Miguel).     

Factorization of fuzzy preferences

In the ordinary framework, the factorization of a weak preference relation into a strict preference relation and an indifference relation is unique. However, in fuzzy set theory, the intersection and the union of fuzzy sets can be represented different ways. Furthermore, some equivalent properties in the ordinary case have generalizations in the fuzzy framework that may be not equivalent. For these reasons there exist in the literature several factorizations of a fuzzy weak preference relation. In this paper we obtain and characterize different factorizations of fuzzy weak preference relations by means of two courses of action which are equivalent in the ordinary framework: axioms and definitions of strict preference and indifference.This work is partially financed by the Junta de Castilla y León (Consejería de Educación y Cultura, Proyecto VA057/02), Ministerio de Ciencia y Tecnología, Plan Nacional de Investigación, Desarrollo e Innovación Tecnológica (I+D+I) (Proyecto BEC2001-2253) and ERDF. I am indebted to José Luis García-Lapresta and an anonymous referee for his helpful comments.     

Iterative elimination of weakly dominated strategies in binary voting agendas with sequential voting

This paper describes the correspondences between the results given by backward induction (BI) and iterative elimination of weakly dominated strategies (IEWDS) in binary voting agendas with sequential voting. When the voters have strict preferences over all candidates, the strategies that survive IEWDS all select the unique candidate selected by the BI strategy profiles. But if some voters are indifferent, this result no longer holds. However, when there are only two candidates, it is possible to demonstrate strong relationships between the results given by BI and IEWDS, even when some voters have indifferences.     

Preferences,the Agenda Setter,and the Distribution of Power in the EU

In this paper, we present a generalization of power indices which includes the preferences of the voters. Using a Multilinear Extension perspective (Owen in Manage Sci 18:p64–p72, 1972a) we measure the probability of the players’ voting “yes” for a particular political issue. Further, we randomize the issues and show the influence that the Agenda Setter can have on a player’s power. We demonstrate these results using data from the European Union to show how the power distribution may shift after enlargement and under the new Constitutional Treaty.     

Does uncertainty lead to sincerity? Simple and complex voting mechanisms

We ask whether the absence of information about other voters’ preferences allows optimal voting to be interpreted as sincere.We start by classifying voting mechanisms as simple and complex according to the number of message types voters can use to elect alternatives. We show that while in simple voting mechanisms the elimination of information about other voters’ preferences allows optimal voting to be interpreted as sincere, this is no longer always true for complex ones. In complex voting mechanisms, voters’ optimal strategy may vary with the size of the electorate. Therefore, in order to interpret optimal voting as sincere for complex voting mechanisms, we describe the optimal voting strategy when voters not only have no information but also have no pivotal power, i.e., as the size of the electorate tends to infinity.     

How frequently do different voting rules encounter voting paradoxes in three-candidate elections?

We estimate the frequencies with which ten voting anomalies (ties and nine voting paradoxes) occur under 14 voting rules, using a statistical model that simulates voting situations that follow the same distribution as voting situations in actual elections. Thus the frequencies that we estimate from our simulated data are likely to be very close to the frequencies that would be observed in actual three-candidate elections. We find that two Condorcet-consistent voting rules do, the Black rule and the Nanson rule, encounter most paradoxes and ties less frequently than the other rules do, especially in elections with few voters. The Bucklin rule, the Plurality rule, and the Anti-plurality rule tend to perform worse than the other eleven rules, especially when the number of voters becomes large.     

Modeling large electorates with Fourier series, with applications to Nash equilibria in proximity and directional models of spatial competition

 In this paper we introduce harmonic analysis (Fourier series) as a tool for characterizing the existence of Nash equilibria in two-dimensional spatial majority rule voting games with large electorates. We apply our methods both to traditional proximity models and to directional models. In the latter voters exhibit preferences over directions rather than over alternatives, per se. A directional equilibrium can be characterized as a Condorcet direction, in analogy to the Condorcet (majority) winner in the usual voting models, i.e., a direction which is preferred by a majority to (or at least is not beaten by) any other direction. We provide a parallel treatment of the total median condition for equilibrium under proximity voting and equilibrium conditions for directional voting that shows that the former result is in terms of a strict equality (a knife-edge result very unlikely to hold) while the latter is in terms of an inequality which is relatively easy to satisfy. For the Matthews [3] directional model and a variant of the Rabinowitz and Macdonald [7] directional model, we present a sufficiency condition for the existence of a Condorcet directional vector in terms of the odd-numbered components of the Fourier series representing the density distribution of the voter points. We interpret our theoretical results by looking at real-world voter distributions and direction fields among voter points derived from U.S. and Norwegian survey data. Received: 7 July 1995 / Accepted: 14 May 1996     

Democratically Elected Aristocracies

The article suggests a formal model of a two-tier voting procedure, which unlike traditional voting systems does not presuppose that every vote counts the same. In deciding a particular issue voters are called in the first round to assign categories of their fellow-citizens with differential voting power (or weights) according to the special position or concern individuals are perceived to have with regard to that issue. In the second stage, voters vote on the issue itself according to their substantive view and their votes are counted in the light of the differential weights assigned in the first round. We analyze formal and philosophical reasons that support the model.     

The two-party system under alternative voting procedures

Countries that elect their policy-makers by means of Plurality Voting tend to have a two-party system. This observation can be explained by the strategic behavior of voters. This article derives two broad classes of voting procedures under which strategic voting behavior induces a two-party system under standard assumptions on voter preferences. One class consists of the voting procedures with unique top-score, i.e., under which a voter can cast a top-score vote for only one candidate (e.g., Plurality Voting, Borda Count). The other class consists of the voting procedures that permit truncated ballots, i.e., under which voters do not have to cast all their votes (e.g., Approval Voting). This analysis suggests that the key for strategic voting behavior to induce a two-party system is that voters can always cast a different score for the two candidates they rank first and second on their ballots.     

On the manipulability of approval voting and related scoring rules

We characterize all preference profiles at which the approval (voting) rule is manipulable, under three extensions of preferences to sets of candidates: by comparison of worst candidates, best candidates, or by comparison based on stochastic dominance. We perform a similar exercise for k-approval rules, where voters approve of a fixed number k of candidates. These results can be used to compare (k-)approval rules with respect to their manipulability. Analytical results are obtained for the case of two voters, specifically, the values of k for which the k-approval rule is minimally manipulable—has the smallest number of manipulable preference profiles—under the various preference extensions are determined. For the number of voters going to infinity, an asymptotic result is that the k-approval rule with k around half the number of candidates is minimally manipulable among all scoring rules. Further results are obtained by simulation and indicate that k-approval rules may improve on the approval rule as far as manipulability is concerned.     

Absorbing and generalized stable sets

Within the framework of an abstract system we establish the existing relationship between the following two solutions: The absorbing sets solution and the generalized stable sets solution.We are grateful to an anonymous referee for helpful comments. Financial support from the project 9/UPV-00035.321-13699/2001 is grateful acknowledged. Inarra gratefully acknowledges the hospitality of Brown University and the financial support from the Ministerio de Educación, Cultura y Deporte, PR 2003-0287.     

Candidate Stability and Voting Correspondences

We extend the analysis of Dutta et al. (in Econometrica, 69:1013–1038, 2001) on strategic candidacy to multivalued environments. For each agenda and each profile of voters’ preferences over running candidates, a voting correspondence selects set of running candidates. A voting correspondence is candidate stable if no candidate ever has an incentive to withdraw her candidacy when all other potential candidates run for office. In the multivalued framework, candidates’ incentives to withdraw depend on candidates’ preferences over sets. If candidates cannot vote and they compare sets of candidates according to their expected utility conditional on some prior probability assessment, then a voting correspondence satisfies candidate stability and unanimity if and only if it is dictatorial. If the probability assessments are restricted to be uniform, candidates’ preferences over sets are consistent with leximin preferences, or candidates can vote, then possibility results are obtained.This paper is a revised version of the second chapter of my Ph.D. Dissertation submitted to the Universitat Autònoma de Barcelona. I am indebted to my supervisor Salvador Barberà for his advice, encouragement, and patience. I thank the hospitality of the Wallis Institute of Political Economy at the University of Rochester, where the revision of this paper was conducted. I am grateful to two anonymous referees and the Associate Editor, John Weymark, for their exhaustive and insightful comments. I also thank Dolors Berga, Carmen Beviá, Walter Bossert, Jernej Čopič, Bhaskar Dutta, Matt Jackson, Jordi Massó, Diego Moreno, David Pérez-Castrillo, and Yves Sprumont for helpful conversations and suggestions. Financial support through Research Grant 1998FI00022 from Comissionat per Universitats i Recerca, Generalitat de Catalunya, Research Project PB98-870 from the Ministerio de Ciencia y Tecnología, Fundación Barrié de la Maza, and Consejería de Innovación, Ciencia y Empresa, Junta de Andalucía is gratefully acknowledged. The usual disclaimer applies.     

Enlargement and the balance of power: an experimental study

Theoretical analysis suggests that enlargement of a voting body may affect the balance of power between the original members even if their number of votes and the decision rule remain constant. Some of the existing voters may actually gain, a phenomenon known as the paradox of new members. We test for this effect using laboratory experiments. Participants propose and vote on how to divide a budget according to weighted majority voting rules, and we measure the voting power of a player by his average payoff in the experiment. By comparing voting power across voting bodies of varying size, we find empirical support for the paradox of new members.     

Power indices and minimal winning coalitions

The Penrose–Banzhaf index and the Shapley–Shubik index are the best-known and the most used tools to measure political power of voters in simple voting games. Most methods to calculate these power indices are based on counting winning coalitions, in particular those coalitions a voter is decisive for. We present a new combinatorial formula how to calculate both indices solely using the set of minimal winning coalitions.     

Voting power: an information theory approach

In recent years, there has been increasing awareness of the importance of formal measures of voting power and of the relevance of such measures to real life political issues. Nevertheless, existing measures have been criticized, especially because of their dependence on the unrealistic assumption that different coalitions have equal probabilities. In this paper we show that the classical problem of measuring voting power can be naturally embedded in information theory. This perspective on voting power allows us to extend measures of voting power to cases in which there are dependencies among voters. In doing so, we distinguish between two different notions of a given voter’s power—‘control’ and ‘informativeness’—corresponding, respectively, to the average uncertainty regarding the outcome of a vote that remains when all others have voted and the average uncertainty that is eliminated when only the given voter has voted. This distinction settles a number of well-known paradoxes and enables the study of voting power on the basis of actual political behavior at all levels.     

Power indices expressed in terms of minimal winning coalitions

A voting situation is given by a set of voters and the rules of legislation that determine minimal requirements for a group of voters to pass a motion. A priori measures of voting power, such as the Shapley–Shubik index and the Banzhaf value, show the influence of the individual players in a voting situation and are calculated by looking at marginal contributions in a simple game consisting of winning and losing coalitions derived from the legislative rules. We introduce a new way to calculate these measures directly from the set of minimal winning coalitions and derive explicit formulae for the Shapley–Shubik and Banzhaf values. This new approach logically appealing as it writes measures as functions of the rules of the legislation. For certain classes of games that arise naturally in applications the logical shortcut drastically simplifies the numerical calculations to obtain the indices. The technique generalises directly to all semivalues.     

Alienation,indifference and the choice of ideological position

In this paper we describe a simple model of individual voting behavior and present its implications for the candidate positioning problem under both vote and plurality maximization. Under our assumptions, some voters at the extremes of the ideological spectrum typically will not vote because they are alienated by the equilibrium location of candidates. There will also be some voters in the middle of the ideological spectrum who will not vote because they are indifferent between the equilibrium locations of the candidates. Both the abstention from alienation and from indifference arise explicitly from utility maximization. Once we allow for alienation and indifference, the two alternative candidate objective functions (vote maximization and plurality maximization) yield different outcomes. In particular, we show that under vote maximization the Median Voter (or Minimum Differentiation) outcome will not arise. On the other hand, under plurality maximization, the Median Voter outcome may or may not hold, depending on the distribution of voter preferences.We should like to thank Jerry Fusselman, Jon Hamilton, Mel Hinich, Charlie Holt and participants at seminars at the University of Virginia, Northwestern University and the 1989 Meetings of the Public Choice Society and the Economic Science Association for their helpful comments.