Simultaneous Elicitation of Committee and Voters' Preferences

Co-localisées avec la Plate-Forme Intelligence Artificielle (PFIA 2019)International audienceSocial choice deals with the problem of determining a consensus choice from the preferences of different voters. In the classical setting, the voting rule is fixed beforehand and full information concerning he preferences of the voters is provided. Recently, the assumption of full preference information has been questioned by a number of researchers and several methods for eliciting preferences have been proposed. In this paper we go one step further and we assume that both the voting rule and the voters’ preferences are partially specified. In this setting, we present an interactive elicitation protocol based on minimax regret and develop several query strategies that interleave questions to the chair and questions to the voters in order to attempt to acquire the most relevant information in order to quickly converge to optimal or a near-optimal alternative

A Local-Dominance Theory of Voting Equilibria

It is well known that no reasonable voting rule is strategyproof. Moreover, the common Plurality rule is particularly prone to strategic behavior of the voters and empirical studies show that people often vote strategically in practice. Multiple game-theoretic models have been proposed to better understand and predict such behavior and the outcomes it induces. However, these models often make unrealistic assumptions regarding voters' behavior and the information on which they base their vote. We suggest a new model for strategic voting that takes into account voters' bounded rationality, as well as their limited access to reliable information. We introduce a simple behavioral heuristic based on \emph{local dominance}, where each voter considers a set of possible world states without assigning probabilities to them. This set is constructed based on prospective candidates' scores (e.g., available from an inaccurate poll). In a \emph{voting equilibrium}, all voters vote for candidates not dominated within the set of possible states. We prove that these voting equilibria exist in the Plurality rule for a broad class of local dominance relations (that is, different ways to decide which states are possible). Furthermore, we show that in an iterative setting where voters may repeatedly change their vote, local dominance-based dynamics quickly converge to an equilibrium if voters start from the truthful state. Weaker convergence guarantees in more general settings are also provided. Using extensive simulations of strategic voting on generated and real preference profiles, we show that convergence is fast and robust, that emerging equilibria are consistent across various starting conditions, and that they replicate widely known patterns of human voting behavior such as Duverger's law. Further, strategic voting generally improves the quality of the winner compared to truthful voting

Parameterized Algorithmics for Computational Social Choice: Nine Research Challenges

Computational Social Choice is an interdisciplinary research area involving Economics, Political Science, and Social Science on the one side, and Mathematics and Computer Science (including Artificial Intelligence and Multiagent Systems) on the other side. Typical computational problems studied in this field include the vulnerability of voting procedures against attacks, or preference aggregation in multi-agent systems. Parameterized Algorithmics is a subfield of Theoretical Computer Science seeking to exploit meaningful problem-specific parameters in order to identify tractable special cases of in general computationally hard problems. In this paper, we propose nine of our favorite research challenges concerning the parameterized complexity of problems appearing in this context

Essays on Delegation and Voter Preferences

Chapter 1 examines delegation and communication as strategies in coordination games with uncertainty and social preferences. I construct a model where other-regarding partners attempt to coordinate over a binary choice with privately known utilities. Players can choose to either communicate by signaling their preferences or delegate the choice entirely to their partner. I characterize equilibrium behavior under various assumptions on information transmission and coordination risk. If coordination is risky, there is a type of first mover advantage where the first player to communicate her own-preference guarantees her ideal outcome when communication is honest revelation. When preference signals are cheap talk, players cannot credibly communicate own-preferences to solve the coordination problem, leading to equilibria where one player always delegates. When coordination is not risky, the game becomes one of pure information transmission where communication is inhibited by strong other-regarding preferences. Chapter 2 presents a model of decision making comparing expertise and altruism as rationales for delegating decision rights. I show that these rationales have different underlying motivations, leading to different predictions in equilibrium delegation. For expertise-driven delegation, a decision maker is more likely to delegate to experts who agree with him. However, this ally principle is not present in altruistic delegation. An altruistic decision maker is more willing to delegate to individuals with whom she disagrees. Chapter 3 presents a theoretic model and the results of a subsequent laboratory experiment to understand voter preferences over leader characteristics. We develop a two-stage model of elections where agents with heterogeneous competence and pro-social preferences must elect a representative entrusted with resources whose growth depends on their competence, but can extract resources for private gain. Voter decisions are informed by observation of candidate competence and decisions in a preceding trust game. A three category representative typology emerges from the model, wherein incentives for performative trustworthiness by crooks are counter-balanced by opportunities for costly signaling by fair and honest candidates. We find support for the models predictions in treatments varying in leader compensation and compulsory contributions to public resources. Incentives for performative trustworthiness result in voters conditionally weighting their decisions towards competence while also serving as a costly signal to earn risk-minimizing voters\u27 benefit of the doubt

Resolving the Complexity of Some Fundamental Problems in Computational Social Choice

This thesis is in the area called computational social choice which is an intersection area of algorithms and social choice theory.Comment: Ph.D. Thesi

Mechanism Choice

This chapter reviews the literature on the selection of regulatory policy instruments, from both normative and positive perspectives. It first reviews the mechanism design literature to identify normative objectives in selecting among the menu or toolbox of policy instruments. The chapter then discusses the public choice and positive political theory literatures and the variety of models developed to attempt to predict the actual selection of alternative policy instruments. It begins with simpler early models focusing on interest group politics and proceeds to more complicated models that incorporate both supply and demand for policy, the role of policy entrepreneurs, behavioral and cognitive choice, and public perceptions and mass politics. It compares these theories to empirical experience. The chapter examines literature in law, economics, political science, and related fields, and it draws examples from US, European, and international regulation. It concludes with suggestions for future research. Document is the author\u27s manuscrip

Mechanism Choice

Mechanism choice can generally be described as the selection of some way to structure rules for social behavior. Nobel Laureate Eric Maskin recently described a mechanism as “an institution, procedure, or game for determining outcomes” (Maskin 2008: 568). In the realm of public law, mechanism choice is synonymous with “instrument choice” or policy design. The selection of the policy instrument can be as important to success or failure as the intended policy outcome. Good intentions or objectives are not enough: the choice of tools matters. A large and growing literature in instrument choice and mechanism design examines both the normative criteria for correcting market failures, matching optimal instruments to different types of problems, minimizing costs, and overcoming incomplete information; and also the positive political factors that may influence the actual selection of instruments, and the pattern of such choices across issue areas, governance systems, and time. Public policy instruments are selected and designed by public bodies –legislatures, executive agencies, and courts – that are comprised of individuals with their own policy preferences, and that are subject to pressures from private interests through lobbying, campaign contributions, and elections. Thus, it is no surprise to the student of public law that the mechanisms actually selected to implement public policy are not necessarily the ones that best pursue the public interest. This chapter begins with a brief summary of normative mechanism choice, including the legal literature on instrument choice and the economics literature on mechanism design. It then moves to a more detailed discussion of positive mechanism choice, also called public choice, political economy, or positive politics. This positive literature explores how political institutions and pressures shape the selection of mechanisms to implement policy, notably when the selected instrument departs from the normative ideal. The positive study of mechanism choice not only informs how political processes shape policy outcomes, but also sheds useful insights into those processes themselves.