A Quantitative Version of the Gibbard-Satterthwaite Theorem for Three Alternatives

05/25/2011

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by   Ehud Friedgut, et al.

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The Gibbard-Satterthwaite theorem states that every non-dictatorial election rule among at least three alternatives can be strategically manipulated. We prove a quantitative version of the Gibbard-Satterthwaite theorem: a random manipulation by a single random voter will succeed with a non-negligible probability for any election rule among three alternatives that is far from being a dictatorship and from having only two alternatives in its range.