Making most voting systems meet the Condorcet criterion reduces their manipulability

François Durand 1, 2 Fabien Mathieu 1, 3 Ludovic Noirie 1, 3
2 GANG - Networks, Graphs and Algorithms
LIAFA - Laboratoire d'informatique Algorithmique : Fondements et Applications, Inria Paris-Rocquencourt
Abstract : Since any non-trivial voting system is susceptible to manipulation, we investigate how it is possible to reduce the set of situations where it is manipulable, that is, such that a coalition of voters, by casting an insincere ballot, may secure an outcome that is better from their point of view. We prove that, for a large class of voting systems, a simple modification allows to reduce manipulability. This modification is Condorcification: when there is a Condorcet winner, designate her; otherwise, use the original rule. Our very general framework allows to do this for any voting system, whatever the form of the original ballots. Hence, when searching for a voting system whose manipulability is minimal, one can restrict to those that meet the Condorcet criterion.
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Submitted on : Tuesday, June 17, 2014 - 1:36:30 PM
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François Durand, Fabien Mathieu, Ludovic Noirie. Making most voting systems meet the Condorcet criterion reduces their manipulability. [Research Report] 2014, pp.27. ⟨hal-01009134⟩

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