Efficient and strategy-proof voting rules: A characterization

The paper provides a characterization of all efficient and strategy-proof voting mechanisms on a large class of preference domains, the class of all generalized single-peaked domains. It is shown that a strategy-proof voting mechanism on such a domain is efficient if and only if it satisfies a weak neutrality condition and is either almost dictatorial, or defined on a median space of dimension less than or equal to two. In more than two dimensions, weakly neutral voting mechanisms are still “locally” efficient.