A tight quantitative version of Arrow's impossibility theorem

نویسنده

  • Nathan Keller
چکیده

The well-known Impossibility Theorem of Arrow asserts that any Generalized Social Welfare Function (GSWF) with at least three alternatives, which satisfies Independence of Irrelevant Alternatives (IIA) and Unanimity and is not a dictatorship, is necessarily nontransitive. In 2002, Kalai asked whether one can obtain the following quantitative version of the theorem: For any > 0, there exists δ = δ( ) such that if a GSWF on three alternatives satisfies the IIA condition and its probability of non-transitive outcome is at most δ, then the GSWF is at most -far from being a dictatorship or from breaching the Unanimity condition. In 2009, Mossel proved such quantitative version, with δ( ) = exp(−C/ ), and generalized it to GSWFs with k alternatives, for all k ≥ 3. In this paper we show that the quantitative version holds with δ( ) = C · , and that this result is tight up to logarithmic factors. Furthermore, our result (like Mossel’s) generalizes to GSWFs with k alternatives. Our proof is based on the works of Kalai and Mossel, but uses also an additional ingredient: a combination of the Bonami-Beckner hypercontractive inequality with a reverse hypercontractive inequality due to Borell, applied to find simultaneously upper bounds and lower bounds on the “noise correlation” between Boolean functions on the discrete cube.

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عنوان ژورنال:
  • CoRR

دوره abs/1003.3956  شماره 

صفحات  -

تاریخ انتشار 2010