Rank aggregation methods for the Web
Proceedings of the 10th international conference on World Wide Web
SIAM Journal on Computing
LATIN'08 Proceedings of the 8th Latin American conference on Theoretical informatics
Using complexity to protect elections
Communications of the ACM
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In this paper we take a new approach to the very old problem of aggregating preferences of multiple agents. We define the notion of popular ranking: a ranking of a set of elements is popular if there exists no other permutation of the elements that a majority of the voters prefer. We show that such a permutation is unlikely to exist: we show that a necessary but not sufficient condition for the existence of a popular ranking is Condorcet's paradox not occurring. In addition, we show that if Condorcet's paradox does not occur, then we can efficiently compute a permutation, which may or may not be popular, but for which the voters will have to solve an NP-hard problem to compute a permutation that a majority of them prefer.