Sincerity and Manipulation under Approval Voting

Under approval voting, each voter can nominate as many candidates as she wishes and the election winners are those candidates that are nominated most often. A voter is said to have voted sincerely if she prefers all those candidates she nominated to all other candidates. As there can be a set of winning candidates rather than just a single winner, a voter’s incentives to vote sincerely will depend on what assumptions we are willing to make regarding the principles by which voters extend their preferences over individual candidates to preferences over sets of candidates. We formulate two such principles, replacement and deletion, and we show that, under approval voting, a voter who accepts those two principles and who knows how the other voters will vote will never have an incentive to vote insincerely. We then discuss the consequences of this result for a number of standard principles of preference extension in view of sincere voting under approval voting

Computational Social Choice: Prospects and Challenges

AbstractHow should we aggregate the individual views of the members of a group so as to arrive at an adequate representation of the collective view of that group? This is a fundamental question of deep philosophical, economic, and political significance that, around the middle of 20th century, has given rise to the field of Social Choice Theory. More recently, a research trend known as Computational Social Choice has emerged, which studies this question from the perspective of Computer Science. This “computational turn” is fuelled both by the fact that questions of social choice have turned out to be central to a range of application areas, notably in the domain of Information and Communication Technologies, and by the insight that many concepts and techniques originating in Computer Science can be used to solve (or provide a new angle on) problems in Social Choice Theory. In this paper, I give a brief introduction to Computational Social Choice and discuss some of the prospects and challenges for this fast growing area of research