« Strategic voting » or manipulability by coalition, occurs when a group of voters can obtain an election outcome they prefer by not voting sincerely. Among the various existing voting systems, Instant-Runoff Voting (IRV) is reputed to be more resistant to strategic voting than others. IRV is used for several presidential and parliamentary elections around the world (Australia, India, Ireland, Papua New Guinea, Sri Lanka). We study the probability that strategic voting is ineffective under IRV when voters randomly draw their preferences among the candidates. This work combines social choice theory, probability, and analytic combinatorics.
Based on joint work with François Durand and Guillem Perarnau
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