Choosing Collectively Optimal Sets of Alternatives Based on the Condorcet Criterion

In elections, an alternative is said to be a Condorcet winner if it is preferred to any other alternative by a majority of voters. While this is a very attractive solution concept, many elections do not have a Condorcet winner. In this paper, we propose a set-valued relaxation of this concept, which we call a Condorcet winning set: such sets consist o f alternatives that collectively dominate any other alternative. We also consider a more general version of this concept, where in stead of domination by a majority of voters we require domination by a given fractio n θ of voters; we refer to this concept as θ winning set. We explore social choice-theoretic and algorithmica spects of these solution concepts, both theoretically and empirically.ouinonouirechercheInternationa