On Strategy-Proof Social Choice between Two Alternatives

Abstract

We study strategy-proof rules for choosing between two alternatives. We consider the full preference domain which allows for indifference. In this framework, for strategy-proof rules, ontoness does not imply efficiency. We weaken the requirement of efficiency to ontoness and characterizes the class of strategy-proof rules. We argue that the notion of efficiency is not desirable always. Our main result provides a simple characterization of the class of onto, anonymous and strategy-proof rules in this framework. Our analysis can help policy makers choose among these rules.