Breaking ties in collective decision making

Abstract

Many classical social preference (multiwinner social choice) correspondences are resolute only when two alternatives and an odd number of individuals are considered. Thus, they generally admit several resolute refinements, each of them naturally interpreted as a tie-breaking rule. In this paper we find out conditions which make a social preference (multiwinner social choice) correspondence admit a resolute refinement fulfilling suitable weak versions of the anonymity and neutrality principles, as well as reversal symmetry (immunity to the reversal bias).