Voting power when using preference ballots

In this paper we provide a generalized power index which gives a measurement of voting power in multi-candidate elections with weighted voting using preference ballots. We use the power index to compare the power of various players between an election using plurality and one using the Borda method. The power index is based upon the Banzhaf power index.     

Ramon Llull: from ‘Ars electionis’ to social choice theory

Ramon Llull (Majorca c.1232–1316) is one of the earliest founding fathers of voting theory and social choice theory. The present article places Llull’s contributions and discussion in the historical context of elections in the medieval Church and the emergence of majority rule as a new general principle for making enforceable collective decisions in replacement of traditional unanimous requirements. To make the majority principle operational, Llull initially proposed a system of exhaustive binary comparisons that is more efficacious in producing a winner than the Condorcet system, in anticipation to the so called Copeland procedure. In contrast to some previous tentative suggestions, careful reading of Llull’s papers demonstrates that he did not propose a rank-order count system, such as those proposed later on by Cusanus and Borda. A new hypothesis is presented to explain Llull’s later proposal of an eliminatory system of partial binary comparisons. Some performance of Llull’s voting systems is estimated by innovative analysis of results in certain modern sports tournaments.     

Why the count de Borda cannot beat the Marquis de Condorcet

Although championed by the Marquis the Condorcet and many others, majority rule has often been rejected as indeterminate, incoherent, or implausible. Majority rule's arch competitor is the Borda count, proposed by the Count de Borda, and there has long been a dispute between the two approaches. In several publications, Donald Saari has recently presented what is arguably the most vigorous and systematic defense of Borda ever developed, a project Saari has supplemented with equally vigorous objections to majority rule. In this article I argue that both Saari's objections to majority rule and his positive case for the Borda count fail. I hold the view that defenders of Condorcet cannot muster arguments to convince supporters of Borda, and vice versa, but here I am only concerned to show that the Count de Borda cannot beat the Marquis de Condorcet. Saari's approach displays what I take to be widespread fallacies in reasoning about social choice worthy of closer analysis. This debate bears on important questions in the philosophy of social choice theory.     

The original Borda count and partial voting

In a Borda count, bc, M. de Borda suggested the last preference cast should receive 1 point, the voter’s penultimate ranking should get 2 points, and so on. Today, however, points are often awarded to (first, second,..., last) preferences cast as per (n, n?1, ..., 1) or more frequently, (n ?1, n?2,..., 0). If partial voting is allowed, and if a first preference is to be given n or n ? 1 points regardless of how many preferences the voter casts, he/she will be incentivised to rank only one option/candidate. If everyone acts in this way, the bc metamorphoses into a plurality vote... which de Borda criticized at length. If all the voters submit full ballots, the outcome—social choice or ranking—will be the same under any of the above three counting procedures. In the event of one or more persons submitting a partial vote, however, outcomes may vary considerably. This preliminary paper suggests research should consider partial voting. The author examines the consequences of the various rules so far advocated and then purports that M. de Borda, in using his formula, was perhaps more astute than the science has hitherto recognised.     

Symmetry extensions of “neutrality” I: Advantage to the condorcet loser

This is the first of three papers introducing a theory for positional voting methods that determines all possible election rankings and relationships that ever could occur with a profile over all possible subsets of candidates for any specified choices of positional voting methods. As such, these results extend to all positional voting systems what was previously possible only for the Borda Count and the plurality voting systems. In this first part certain mathematical symmetries based on neutrality are used 1) to generalize the basic properties that cause the desired features of the Borda Count and 2) to describe classes of positional voting methods with new types of election relationships among the election outcomes. Some of these relationships generalize the well-known results about the positioning of a Condorcet winner/loser within a Borda ranking, but now it is possible for the Condorcet loser, rather than the winner, to have the advantage to win certain positional elections. Included among the results are axiomatic characterizations of many positional voting methods.This research was supported in part by NSF Grant IRI-9103180.     

A nail-biting election

In the first competitive election for President of the Social Choice and Welfare Society, the (official) approval-voting winner differed from the (hypothetical) Borda count winner, who was also the Condorcet winner. But because the election was essentially a toss-up, it is impossible to say who should have won. The election for Council was more true to form of other professional-society elections, with the winners identical, and even their rankings almost duplicative, under both voting systems. Received: 11 April 2000/Accepted: 26 March 2001     

Nash implementable domains for the Borda count

We characterize the preference domains on which the Borda count satisfies Maskin monotonicity. The basic concept is the notion of a “cyclic permutation domain” which arises by fixing one particular ordering of alternatives and including all its cyclic permutations. The cyclic permutation domains are exactly the maximal domains on which the Borda count is strategy-proof when combined with every possible tie breaking rule. It turns out that the Borda count is monotonic on a larger class of domains. We show that the maximal domains on which the Borda count satisfies Maskin monotonicity are the “cyclically nested permutation domains” which are obtained from the cyclic permutation domains in an appropriately specified recursive way. We thank József Mala for posing the question of Nash implementability on restricted domains that led to this research. We are very grateful to two anonymous referees and an associate editor for their helpful comments and suggestions. The second author gratefully acknowledges financial support from the Hungarian Academy of Sciences (MTA) through the Bolyai János research fellowship.     

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.     

The sensitivity of weight selection on the Condorcet efficiency of weighted scoring rules

A weighted scoring rule, Rule λ, on three alternative elections selects the winner by awarding 1 point to each voter's first ranked candidate, λ points to the second ranked candidate, and zero to the third ranked candidate. The Condorcet winner is the candidate that would defeat each other candidate in a series of pairwise elections by majority rule. The Condorcet efficiency of Rule λ is the conditional probability that Rule λ selects the Condorcet winner, given that a Condorcet winner exists. Borda rule (λ=1/2) is the weighted scoring rule that maximizes Condorcet efficiency. The current study considers the conditional probability that Borda rule selects the Rule λ winner, given that Rule λ elects the Condorcet winner with a large electorate. Received: 21 August 1996 / Accepted: 7 January 1997     

Preference intensity representation: strategic overstating in large elections

If voters vote strategically, is it useful to offer them the possibility of expressing nuanced opinions, or would they always overstate the intensity of their preferences? For additive voting rules, say that a ballot is extremal if it is neither abstention-like nor can be expressed as a mixture of the available ballots. We give a sufficient condition for strategic equivalence: if two rules share the same set of extremal ballots (up to an homothetic transformation), they are strategically equivalent in large elections. This condition is also necessary for the strategic equivalence of positional rules. These results do not hold for small electorates.     

The borda and condorcet principles: Three medieval applications

We report three medieval works, hitherto unknown to social choice, which discuss procedures for elections when there are more than two candidates. Two of the three propose Borda methods and the third a Condorcet method of successive pairwise comparison. All three discuss problems of manipulation. One of them displays a matrix for pairwise comparisons; this is a work written in 1299, nearly 600 years before the matrix notation was believed to have been invented by C. L. Dodgson. We conclude with a review of the theory of voting in medieval Europe.We acknowledge with gratitude the support of the Leverhulme Trust for IMcL's work on the history of social choice; William Riker for an initial lead on Nicolas Cusanus; Alexander Murray for translating Cusanus and reviewing IMcL's translation of Lull's Latin text; and Robert Pring-Mill for reviewing JL's translation of Lull's Catalan text.     

An experiment on coordination in multi-candidate elections: The importance of polls and election histories

Do polls simply measure intended voter behavior or can they affect it and, thus, change election outcomes? Do candidate ballot positions or the results of previous elections affect voter behavior? We conduct several series of experimental, three-candidate elections and use the data to provide answers to these questions. In these elections, we pay subjects conditionally on election outcomes to create electorates with publicly known preferences. A majority (but less than two-thirds) of the voters are split in their preferences between two similar candidates, while a minority (but plurality) favor a third, dissimilar candidate. If all voters voted sincerely, the third candidate — a Condorcet loser — would win the elections. We find that pre-election polls significantly reduce the frequency with which the Condorcet loser wins. Further, the winning candidate is usually the majority candidate who is listed first on the poll and election ballots. The evidence also shows that a shared history enables majority voters to coordinate on one of their favored candidates in sequences of identical elections. With polls, majority-preferred candidates often alternate as election winners.     

The Borda dictionary

Forn candidates, a profile of voters defines a unique Borda election ranking for each of the 2 ⁿ – (n + 1) subsets of two or more candidates. The Borda Dictionary is the set of all of these election listings that occur for any choice of a profile. As such, the dictionary contains all positive features, all flaws, and all paradoxes that can occur with single profile, sincere Borda elections. After the Borda Dictionary is characterized, it is used to show in what ways the Borda Count (BC) is an improvement over other positional voting methods and to derive several new BC properties. These properties include several new characterizations of the BC expressed in terms of axiomatic representations of social choice functions, as well as showing, for example, that the BC ranking ofn candidates can be uniquely determined by the BC rankings of all sets ofk <n candidates for any choice ofk between 2 andn.This research was supported, in part, by NSF grants IRI8415348, IRI-8803505 and a Fellowship from the Guggenheim Memorial Foundation.     

Strategic voting and nomination

Using computer simulations based on three separate data generating processes, I estimate the fraction of elections in which sincere voting is a core equilibrium given each of eight single-winner voting rules. Additionally, I determine how often each rule is vulnerable to simple voting strategies such as ‘burying’ and ‘compromising’, and how often each rule gives an incentive for non-winning candidates to enter or leave races. I find that Hare is least vulnerable to strategic voting in general, whereas Borda, Coombs, approval, and range are most vulnerable. I find that plurality is most vulnerable to compromising and strategic exit (causing an unusually strong tendency toward two-party systems), and that Borda is most vulnerable to strategic entry. I use analytical proofs to provide further intuition for some of my key results.     

The paradox of multiple elections

Assume that voters must choose between voting yes (Y) and voting no (N) on three propositions on a referendum. If the winning combination is NYY on the first, second, and third propositions, respectively, the paradox of multiple elections is that NYY can receive the fewest votes of the 2³ = 8 combinations. Several variants of this paradox are illustrated, and necessary and sufficient conditions for its occurrence, related to the “incoherence” of support, are given. The paradox is shown, via an isomorphism, to be a generalization of the well-known paradox of voting. One real-life example of the paradox involving voting on propositions in California, in which not a single voter voted on the winning side of all the propositions, is given. Several empirical examples of variants of the paradox that manifested themselves in federal elections – one of which led to divided government – and legislative votes in the US House of Representatives, are also analyzed. Possible normative implications of the paradox, such as allowing voters to vote directly for combinations using approval voting or the Borda count, are discussed. Received: 31 July 1996 / Accepted: 1 October 1996     

Multiple votes,ballot truncation and the two-party system: an experiment

Duverger’s law states that Plurality Voting tends to favor a two-party system. We conducted laboratory experiments to study whether voting procedures other than Plurality Voting could favor a two-party system as well. Plurality Voting is compared with Approval Voting and Dual Voting, both of which allow to vote for multiple candidates, but differ in whether voters are required to cast all their votes. We find that in most elections held under Plurality Voting and Approval Voting, at most two candidates are viable. By contrast, three candidates are viable in a sizable number of elections held under Dual Voting due to strategic voting. Our evidence suggests that Approval Voting may encourage a two-party system, whereas Dual Voting may encourage multipartism. The voters’ ability to truncate ballots (i.e., not cast all their votes) is essential for supporting the two-party system under Approval Voting.     

The Borda count and agenda manipulation

A standard objection to the Borda count, as an actual voting procedure, is that it is subject to agenda manipulation. The classical example is the introduction, in order to favour a candidate or option y, of a new option z ranked on every voter's preference scale immediately below y; y may as a result obtain the highest Borda count, although, if z had not been introduced, a different option would have done so. Strategic use of this device is not greatly to be feared, but it does point to a defect in the system: equating the distance on each voter's preference scale between any option and the next imposes a penalty for dissimilarity. The corrective is to vary the distances by introducing a measure of dissimilarity, as perceived by the voters and revealed by their preference scales. Two possible ways of doing this are described, yielding revised and adjusted Borda scores. It is shown by examples that these will often, but not always, undo the `agenda manipulation' effect, and questioned whether it is desirable to undo it altogether. Received: 22 August 1996/Accepted: 31 October 1996     

Two field experiments on Approval Voting in Germany

We report on two field experiments on Approval Voting conducted during actual state and federal elections in Germany. Voters provided approval ballots both for named district candidates and for state parties. The data reveal significant discrepancies in the outcomes under the official method and Approval Voting. Further, our analysis suggests that currently used voting methods do a poor job of representing the electorate??s preferences. As a consequence, some recurring features of the political landscape in a given country might be, in part, an artifice of the employed voting method.     

Some Further Results on the Manipulability of Social Choice Rules

A typology of electoral environments in which strategic manipulation of voting rules can occur is proposed. From this typology, six different concepts of equilibria (or quasi-equilibria) are defined, including the usual ones. Then, focusing on three alternative elections, we derive some analytical representations for the vulnerability of a large number of voting rules to strategic manipulation by considering successively each type of equilibrium. Our results show that the hierarchy of the rules changes when the voting framework is modified. However, some rules are clearly dominated and some others (among which the Borda and the Nanson rules) appear to be uniquely the best in some specific contexts.     

Manipulability measures of common social choice functions

All social choice functions are manipulable when more than two alternatives are available. I evaluate the manipulability of the Borda count, plurality rule, minimax set, and uncovered set. Four measures of manipulability are defined and computed stochastically for small numbers of agents and alternatives.  Social choice rules derived from the minimax and uncovered sets are found to be relatively immune to manipulation whether a sole manipulating agent has complete knowledge or absolutely no knowledge of the preferences of the others. The Borda rule is especially manipulable if the manipulating agent has complete knowledge of the others. Received: 5 January 1996/Accepted: 31 July 1998