An Optimal Single-Winner Preferential Voting System Based on Game Theory
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Approval Voting Under Dichotomous Preferences: a Catalogue of Characterizations
Draft – June 25, 2021 Approval Voting under Dichotomous Preferences: A Catalogue of Characterizations Florian Brandl Dominik Peters University of Bonn Harvard University [email protected] [email protected] Approval voting allows every voter to cast a ballot of approved alternatives and chooses the alternatives with the largest number of approvals. Due to its simplicity and superior theoretical properties it is a serious contender for use in real-world elections. We support this claim by giving eight characterizations of approval voting. All our results involve the reinforcement axiom, which requires choices to be consistent across different electorates. In addition, we consider strategyproofness, consistency with majority opinions, consistency under cloning alternatives, and invariance under removing inferior alternatives. We prove our results by reducing them to a single base theorem, for which we give a simple and intuitive proof. 1 Introduction Around the world, when electing a leader or a representative, plurality is by far the most common voting system: each voter casts a vote for a single candidate, and the candidate with the most votes is elected. In pioneering work, Brams and Fishburn (1983) proposed an alternative system: approval voting. Here, each voter may cast votes for an arbitrary number of candidates, and can thus choose whether to approve or disapprove of each candidate. The election is won by the candidate who is approved by the highest number of voters. Approval voting allows voters to be more expressive of their preferences, and it can avoid problems such as vote splitting, which are endemic to plurality voting. Together with its elegance and simplicity, this has made approval voting a favorite among voting theorists (Laslier, 2011), and has led to extensive research literature (Laslier and Sanver, 2010). -
A Treasury System for Cryptocurrencies: Enabling Better Collaborative Intelligence ⋆
A Treasury System for Cryptocurrencies: Enabling Better Collaborative Intelligence ? Bingsheng Zhang1, Roman Oliynykov2, and Hamed Balogun3 1 Lancaster University, UK [email protected] 2 Input Output Hong Kong Ltd. [email protected] 3 Lancaster University, UK [email protected] Abstract. A treasury system is a community controlled and decentralized collaborative decision- making mechanism for sustainable funding of the blockchain development and maintenance. During each treasury period, project proposals are submitted, discussed, and voted for; top-ranked projects are funded from the treasury. The Dash governance system is a real-world example of such kind of systems. In this work, we, for the first time, provide a rigorous study of the treasury system. We modelled, designed, and implemented a provably secure treasury system that is compatible with most existing blockchain infrastructures, such as Bitcoin, Ethereum, etc. More specifically, the proposed treasury system supports liquid democracy/delegative voting for better collaborative intelligence. Namely, the stake holders can either vote directly on the proposed projects or delegate their votes to experts. Its core component is a distributed universally composable secure end-to-end verifiable voting protocol. The integrity of the treasury voting decisions is guaranteed even when all the voting committee members are corrupted. To further improve efficiency, we proposed the world's first honest verifier zero-knowledge proof for unit vector encryption with logarithmic size communication. This partial result may be of independent interest to other cryptographic protocols. A pilot system is implemented in Scala over the Scorex 2.0 framework, and its benchmark results indicate that the proposed system can support tens of thousands of treasury participants with high efficiency. -
Game Theory and Democracy Homework Problems
Game Theory and Democracy Homework Problems PAGE 82 Challenge Problem: Show that any voting model (such as the Unit Interval Model or the Unit Square Model) which has a point symmetry always has a Condorcet winner for every election, namely the candidate who is closest to the point of symmetry! PAGE 93 Exercise: Show that if there are not any cycles of any length in the preferences of the voters, then there must be a Condorcet winner. (Don’t worry about making your proof rigorous, just convince yourself of this fact, to the point you could clearly explain your ideas to someone else.) PAGE 105 Exercise: Prove that the strongest chain strength of a chain from Candidate Y to Candidate X is 3. (If you can convince a skeptical friend that it is true, then that is a proof.) Exercise: Prove that it is never necessary to use a candidate more than once to find a chain with the strongest chain strength between two candidates. Hint: Show that whenever there is a loop, like the one shown in red Y (7) Z (3) W (9) Y (7) Z (3) W (11) X, we can consider a shortened chain by simply deleting the red loop Y (7) Z (3) W (11) X which is at least as strong as the original loop. Exercises: Prove that all of the chains above are in fact strongest chains, as claimed. Hint: The next figure, which has all of the information of the margin of victory matrix, will be useful, and is the type of figure you may choose to draw for yourself for other elections, from time to time. -
Crowdsourcing Applications of Voting Theory Daniel Hughart
Crowdsourcing Applications of Voting Theory Daniel Hughart 5/17/2013 Most large scale marketing campaigns which involve consumer participation through voting makes use of plurality voting. In this work, it is questioned whether firms may have incentive to utilize alternative voting systems. Through an analysis of voting criteria, as well as a series of voting systems themselves, it is suggested that though there are no necessarily superior voting systems there are likely enough benefits to alternative systems to encourage their use over plurality voting. Contents Introduction .................................................................................................................................... 3 Assumptions ............................................................................................................................... 6 Voting Criteria .............................................................................................................................. 10 Condorcet ................................................................................................................................. 11 Smith ......................................................................................................................................... 14 Condorcet Loser ........................................................................................................................ 15 Majority ................................................................................................................................... -
Computational Perspectives on Democracy
Computational Perspectives on Democracy Anson Kahng CMU-CS-21-126 August 2021 Computer Science Department School of Computer Science Carnegie Mellon University Pittsburgh, PA 15213 Thesis Committee: Ariel Procaccia (Chair) Chinmay Kulkarni Nihar Shah Vincent Conitzer (Duke University) David Pennock (Rutgers University) Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy. Copyright c 2021 Anson Kahng This research was sponsored by the National Science Foundation under grant numbers IIS-1350598, CCF- 1525932, and IIS-1714140, the Department of Defense under grant number W911NF1320045, the Office of Naval Research under grant number N000141712428, and the JP Morgan Research grant. The views and conclusions contained in this document are those of the author and should not be interpreted as representing the official policies, either expressed or implied, of any sponsoring institution, the U.S. government or any other entity. Keywords: Computational Social Choice, Theoretical Computer Science, Artificial Intelligence For Grandpa and Harabeoji. iv Abstract Democracy is a natural approach to large-scale decision-making that allows people affected by a potential decision to provide input about the outcome. However, modern implementations of democracy are based on outdated infor- mation technology and must adapt to the changing technological landscape. This thesis explores the relationship between computer science and democracy, which is, crucially, a two-way street—just as principles from computer science can be used to analyze and design democratic paradigms, ideas from democracy can be used to solve hard problems in computer science. Question 1: What can computer science do for democracy? To explore this first question, we examine the theoretical foundations of three democratic paradigms: liquid democracy, participatory budgeting, and multiwinner elections. -
An Optimal Single-Winner Preferential Voting System Based on Game Theory∗
An Optimal Single-Winner Preferential Voting System Based on Game Theory∗ Ronald L. Rivest and Emily Shen Abstract • The election winner is determined by a random- ized method, based for example on the use of We present an optimal single-winner preferential vot- ten-sided dice, that picks outcome x with prob- ing system, called the \GT method" because of its in- ability p∗(x). If there is a Condorcet winner x, teresting use of symmetric two-person zero-sum game then p∗(x) = 1, and no dice are needed. We theory to determine the winner. Game theory is not also briefly discuss a deterministic variant of GT, used to describe voting as a multi-player game be- which we call GTD. tween voters, but rather to define when one voting system is better than another one. The cast ballots The GT system, essentially by definition, is opti- determine the payoff matrix, and optimal play corre- mal: no other voting system can produce election sponds to picking winners optimally. outcomes that are liked better by the voters, on the The GT method is quite simple and elegant, and average, than those of the GT system. We also look works as follows: at whether the GT system has several standard prop- erties, such as monotonicity, consistency, etc. • Voters cast ballots listing their rank-order pref- The GT system is not only theoretically interest- erences of the alternatives. ing and optimal, but simple to use in practice; it is probably easier to implement than, say, IRV. We feel • The margin matrix M is computed so that for that it can be recommended for practical use. -
Instructor's Manual
The Mathematics of Voting and Elections: A Hands-On Approach Instructor’s Manual Jonathan K. Hodge Grand Valley State University January 6, 2011 Contents Preface ix 1 What’s So Good about Majority Rule? 1 Chapter Summary . 1 Learning Objectives . 2 Teaching Notes . 2 Reading Quiz Questions . 3 Questions for Class Discussion . 6 Discussion of Selected Questions . 7 Supplementary Questions . 10 2 Perot, Nader, and Other Inconveniences 13 Chapter Summary . 13 Learning Objectives . 14 Teaching Notes . 14 Reading Quiz Questions . 15 Questions for Class Discussion . 17 Discussion of Selected Questions . 18 Supplementary Questions . 21 3 Back into the Ring 23 Chapter Summary . 23 Learning Objectives . 24 Teaching Notes . 24 v vi CONTENTS Reading Quiz Questions . 25 Questions for Class Discussion . 27 Discussion of Selected Questions . 29 Supplementary Questions . 36 Appendix A: Why Sequential Pairwise Voting Is Monotone, and Instant Runoff Is Not . 37 4 Trouble in Democracy 39 Chapter Summary . 39 Typographical Error . 40 Learning Objectives . 40 Teaching Notes . 40 Reading Quiz Questions . 41 Questions for Class Discussion . 42 Discussion of Selected Questions . 43 Supplementary Questions . 49 5 Explaining the Impossible 51 Chapter Summary . 51 Error in Question 5.26 . 52 Learning Objectives . 52 Teaching Notes . 53 Reading Quiz Questions . 54 Questions for Class Discussion . 54 Discussion of Selected Questions . 55 Supplementary Questions . 59 6 One Person, One Vote? 61 Chapter Summary . 61 Learning Objectives . 62 Teaching Notes . 62 Reading Quiz Questions . 63 Questions for Class Discussion . 65 Discussion of Selected Questions . 65 CONTENTS vii Supplementary Questions . 71 7 Calculating Corruption 73 Chapter Summary . 73 Learning Objectives . 73 Teaching Notes . -
Selecting the Runoff Pair
Selecting the runoff pair James Green-Armytage New Jersey State Treasury Trenton, NJ 08625 [email protected] T. Nicolaus Tideman Department of Economics, Virginia Polytechnic Institute and State University Blacksburg, VA 24061 [email protected] This version: May 9, 2019 Accepted for publication in Public Choice on May 27, 2019 Abstract: Although two-round voting procedures are common, the theoretical voting literature rarely discusses any such rules beyond the traditional plurality runoff rule. Therefore, using four criteria in conjunction with two data-generating processes, we define and evaluate nine “runoff pair selection rules” that comprise two rounds of voting, two candidates in the second round, and a single final winner. The four criteria are: social utility from the expected runoff winner (UEW), social utility from the expected runoff loser (UEL), representativeness of the runoff pair (Rep), and resistance to strategy (RS). We examine three rules from each of three categories: plurality rules, utilitarian rules and Condorcet rules. We find that the utilitarian rules provide relatively high UEW and UEL, but low Rep and RS. Conversely, the plurality rules provide high Rep and RS, but low UEW and UEL. Finally, the Condorcet rules provide high UEW, high RS, and a combination of UEL and Rep that depends which Condorcet rule is used. JEL Classification Codes: D71, D72 Keywords: Runoff election, two-round system, Condorcet, Hare, Borda, approval voting, single transferable vote, CPO-STV. We are grateful to those who commented on an earlier draft of this paper at the 2018 Public Choice Society conference. 2 1. Introduction Voting theory is concerned primarily with evaluating rules for choosing a single winner, based on a single round of voting. -
Rangevote.Pdf
Smith typeset 845 Sep 29, 2004 Range Voting Range voting Warren D. Smith∗ [email protected] December 2000 Abstract — 3 Compact set based, One-vote, Additive, The “range voting” system is as follows. In a c- Fair systems (COAF) 3 candidate election, you select a vector of c real num- 3.1 Non-COAF voting systems . 4 bers, each of absolute value ≤ 1, as your vote. E.g. you could vote (+1, −1, +.3, −.9, +1) in a 5-candidate 4 Honest Voters and Utility Voting 5 election. The vote-vectors are summed to get a c- ~x i xi vector and the winner is the such that is maxi- 5 Rational Voters and what they’ll generi- mum. cally do in COAF voting systems 5 Previously the area of voting systems lay under the dark cloud of “impossibility theorems” showing that no voting system can satisfy certain seemingly 6 A particular natural compact set P 6 reasonable sets of axioms. But I now prove theorems advancing the thesis 7 Rational voting in COAF systems 7 that range voting is uniquely best among all possi- ble “Compact-set based, One time, Additive, Fair” 8 Uniqueness of P 8 (COAF) voting systems in the limit of a large num- ber of voters. (“Best” here roughly means that each 9 Comparison with previous work 10 voter has both incentive and opportunity to provide 9.1 How range voting behaves with respect to more information about more candidates in his vote Nurmi’s list of voting system problems . 10 than in any other COAF system; there are quantities 9.2 Some other properties voting systems may uniquely maximized by range voting.) have .................... -
Chapter 3 Voting Systems
Chapter 3 Voting Systems 3.1 Introduction We rank everything. We rank movies, bands, songs, racing cars, politicians, professors, sports teams, the plays of the day. We want to know “who’s number one?” and who isn't. As a lo- cal sports writer put it, “Rankings don't mean anything. Coaches continually stress that fact. They're right, of course, but nobody listens. You know why, don't you? People love polls. They absolutely love ’em” (Woodling, December 24, 2004, p. 3C). Some rankings are just for fun, but people at the top sometimes stand to make a lot of money. A study of films released in the late 1970s and 1980s found that, if a film is one of the 5 finalists for the Best Picture Oscar at the Academy Awards, the publicity generated (on average) generates about $5.5 mil- lion in additional box office revenue. Winners make, on average, $14.7 million in additional revenue (Nelson et al., 2001). In today's inflated dollars, the figures would no doubt be higher. Actors and directors who are nominated (and who win) should expect to reap rewards as well, since the producers of new films are eager to hire Oscar-winners. This chapter is about the procedures that are used to decide who wins and who loses. De- veloping a ranking can be a tricky business. Political scientists have, for centuries, wrestled with the problem of collecting votes and moulding an overall ranking. To the surprise of un- 1 CHAPTER 3. VOTING SYSTEMS 2 dergraduate students in both mathematics and political science, mathematical concepts are at the forefront in the political analysis of voting procedures. -
Explaining All Three-Alternative Voting Outcomes*
Journal of Economic Theory 87, 313355 (1999) Article ID jeth.1999.2541, available online at http:ÂÂwww.idealibrary.com on Explaining All Three-Alternative Voting Outcomes* Donald G. Saari Department of Mathematics, Northwestern University, Evanston, Illinois 60208-2730 dsaariÄnwu.edu Received January 12, 1998; revised April 13, 1999 A theory is developed to explain all possible three-alternative (single-profile) pairwise and positional voting outcomes. This includes all preference aggregation paradoxes, cycles, conflict between the Borda and Condorcet winners, differences among positional outcomes (e.g., the plurality and antiplurality methods), and dif- ferences among procedures using these outcomes (e.g., runoffs, Kemeny's rule, and Copeland's method). It is shown how to identify, interpret, and construct all profiles supporting each paradox. Among new conclusions, it is shown why a standard for the field, the Condorcet winner, is seriously flawed. Journal of Economic Literature Classification Numbers: D72, D71. 1999 Academic Press 1. INTRODUCTION Over the last two centuries considerable attention has focussed on the properties of positional voting procedures. These commonly used approaches assign points to alternatives according to how each voter posi- tions them. The standard plurality method, for instance, assigns one point to a voter's top-ranked candidate and zero to all others, while the Borda count (BC) assigns n&1, n&2, ..., n&n=0 points, respectively, to a voter's first, second, ..., nth ranked candidate. The significance of these pro- cedures derives from their wide usage, but their appeal comes from their mysterious paradoxes (i.e., counterintuitive conclusions) demonstrating highly complex outcomes. By introducing doubt about election outcomes, these paradoxes raise the legitimate concern that, inadvertently, we can choose badly even in sincere elections. -
An Analysis of Random Elections with Large Numbers of Voters Arxiv
An Analysis of Random Elections with Large Numbers of Voters∗ Matthew Harrison-Trainor September 8, 2020 Abstract In an election in which each voter ranks all of the candidates, we consider the head- to-head results between each pair of candidates and form a labeled directed graph, called the margin graph, which contains the margin of victory of each candidate over each of the other candidates. A central issue in developing voting methods is that there can be cycles in this graph, where candidate A defeats candidate B, B defeats C, and C defeats A. In this paper we apply the central limit theorem, graph homology, and linear algebra to analyze how likely such situations are to occur for large numbers of voters. There is a large literature on analyzing the probability of having a majority winner; our analysis is more fine-grained. The result of our analysis is that in elections with the number of voters going to infinity, margin graphs that are more cyclic in a certain precise sense are less likely to occur. 1 Introduction The Condorcet paradox is a situation in social choice theory where every candidate in an election with three or more alternatives would lose, in a head-to-head election, to some other candidate. For example, suppose that in an election with three candidates A, B, and C, and three voters, the voter's preferences are as follows: arXiv:2009.02979v1 [econ.TH] 7 Sep 2020 First choice Second choice Third choice Voter 1 A B C Voter 2 B C A Voter 3 C A B There is no clear winner, for one can argue that A cannot win as two of the three voters prefer C to A, that B cannot win as two of the three voters prefer A to B, and that C cannot win as two of the three voters prefer B to C.