Approximability of Dodgson's rule

Abstract

It is known that Dodgson's rule is computationally very demanding. Tideman (1987) suggested an approximation to it but did not investigate how often his approximation selects the Dodgson winner. We show that under the Impartial Culture assumption the probability that that the another approximation - we call it Dodgson Quick - for which thisconvergence of this probability to 1 is slow. We suggest convergence is exponentially fast. Also we show that Simpson and Dodgson rules are asymptotically different. We formulate, and heavily use in construction of examples, the generalization of McGarvey's theorem (1953) for weighted majority relations.