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ATAL
2008
Springer

Copeland voting: ties matter

9 years 6 days ago
Copeland voting: ties matter
We study the complexity of manipulation for a family of election systems derived from Copeland voting via introducing a parameter that describes how ties in head-to-head contests are valued. We show that the thus obtained problem of manipulation for unweighted Copeland elections is NP-complete even if the size of the manipulating coalition is limited to two. Our result holds for all rational values of such that 0 < < 1 except for = 1 2 . Since it is well known that manipulation via a single voter is easy for Copeland, our result is the first one where an election system originally known to be vulnerable to manipulation via a single voter is shown to be resistant to manipulation via a coalition of a constant number of voters. We also study the complexity of manipulation for Copeland for the case of a constant number of candidates. We show that here the exact complexity of manipulation often depends closely on the : Depending on whether we try to make our favorite candidate a ...
Piotr Faliszewski, Edith Hemaspaandra, Henning Sch
Added 12 Oct 2010
Updated 12 Oct 2010
Type Conference
Year 2008
Where ATAL
Authors Piotr Faliszewski, Edith Hemaspaandra, Henning Schnoor
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