07431 Abstracts Collection -- Computational Issues in Social Choice

From the 21st to the 26th of October 2007, the Dagstuhl Seminar 07431 on ``Computational Issues in Social Choice\u27\u27 was held at the International Conference and Research Center (IBFI), Schloss Dagstuhl. During the seminar, several participants presented their recent research, and ongoing work and open problems were discussed. The abstracts of the talks given during the seminar are collected in this paper. The first section summarises the seminar topics and goals in general. Links to full papers are provided where available

The Communication Burden of Single Transferable Vote, in Practice

We study single-winner STV from the point of view of communication. First, we assume that voters give, in a single shot, their top-k alternatives; we define a version of STV that works for such votes, and we evaluate empirically the extent to which it approximates the standard STV rule. Second, we evaluate empirically the communication cost of the protocol for STV defined by Conitzer and Sandholm (2005) and some of its improvements

Single Transferable Vote: Incomplete Knowledge and Communication Issues

International audienceSingle Transferable Vote (STV) is used in large political elections around the world. It is easy to understand and has desirable normative properties such as clone-proofness. However, voters need to report full rankings, which can make it less practical than plurality voting. We study ways to minimize the amount of communication required to use single-winner STV. In the first part of the paper, voters are assumed to report their top-k alternatives in a single shot. We empirically evaluate the extent to which STV with truncated ballots approximates STV with full information. We also study the computational complexity of the possible winner problem for top-k ballots. For $k=1$, it can be solved in polynomial time, but is NP-complete when $k\geq 2$. In the second part, we consider interactive communication protocols for STV. Building on a protocol proposed by Conitzer and Sandholm (2005), we show how we can reduce the amount of communication required in practice. We then study empirically the average communication complexity of these protocols, based on randomly generated profiles, and on real-world election data. Our conclusion is that STV needs, in practice, much less information than in the worst case

Campaign Management under Approval-Driven Voting Rules

Approval-like voting rules, such as Sincere-Strategy Preference-Based Approval voting (SP-AV), the Bucklin rule (an adaptive variant of $k$-Approval voting), and the Fallback rule (an adaptive variant of SP-AV) have many desirable properties: for example, they are easy to understand and encourage the candidates to choose electoral platforms that have a broad appeal. In this paper, we investigate both classic and parameterized computational complexity of electoral campaign management under such rules. We focus on two methods that can be used to promote a given candidate: asking voters to move this candidate upwards in their preference order or asking them to change the number of candidates they approve of. We show that finding an optimal campaign management strategy of the first type is easy for both Bucklin and Fallback. In contrast, the second method is computationally hard even if the degree to which we need to affect the votes is small. Nevertheless, we identify a large class of scenarios that admit fixed-parameter tractable algorithms.Comment: 34 pages, 1 figur

Essays on Collective Action

This dissertation comprises 3 chapters dealing with collective action. Chapter 1 explores the behavior of individuals who face the provision of a public good that requires a minimal amount of aggregate contributions. Using a laboratory experiment we show that, unlike in the provision of linear public goods, an endogenous move order of players does not improve cooperation rates and payoffs. We also identify a specific externality: When observing unfair contributions, players wait for the contributions of others and thereby leave their group members uninformed about their willingness to contribute. Chapter 2 studies the valuation of bundles of public and private goods, such as sustainably fished seafood, certified wood products, or green electricity. We analyze individuals' willingness to pay (WTP) for a private good, a cup, and a public good, a donation to a charity. In an experiment we offer the goods either as a bundle or separately. Our data show that the WTP for the bundle exceeds the WTP for the separately offered public and private good. A review of several behavioral concepts suggests behavior consistent with the data. Chapter 3 analyzes how the political system affects campaigns of political candidates and the voters' capacity to empower competent politicians. Our model shows that variations in power concentration involve a trade-off. On the one hand, higher power concentration enables the voters' preferred politician to enforce larger parts of his agenda. On the other hand, higher power concentration increases electoral stakes and distorts politicians' campaigns. We identify a negative relation between the optimal level of power concentration and the extent of politicians' office motivation. The results of an empirical analysis are in line with this prediction

Behavioral Economics: Past, Present, Future

Behavioral economics increases the explanatory power of economics by providing it with more realistic psychological foundations. This book consists of representative recent articles in behavioral economics. This chapter is intended to provide an introduction to the approach and methods of behavioral economics, and to some of its major findings, applications, and promising new directions. It also seeks to fill some unavoidable gaps in the chapters’ coverage of topics

Essays on Labor and Behavioral Economics

This dissertation includes three essays on topics in labor and behavioral economics. The first chapter studies a long-lasting question in labor, namely if public-sector workers are paid more than their counterfactual wages in the private sector. The second chapter experimentally studies the problem of adverse selection occurring over time. Finally, the third chapter examines decision-making when agents become aware of hitherto unknown contingencies, also using experimental methods