An Investigation of Weak-Veto Rules in Preference Aggregation

A new class of preference-aggregation rules is proposed, weak-veto rules. Weak-veto rules are applicable in settings characterized by strong pre-existing views on the desirability of different outcomes, whose recommendations should be modified only in the presence of strenuous opposition. They are characterized by strategy-proofness, strong efficiency, and unanimity-basedness. When non-manipulability requirements are strengthened to K-strategy-proofness, the positive results are weakened, except for the case of three alternatives and a sub-class of weak-veto rules based on Kemeny distances. This demonstrates the compatibility of stronger efficiency and non-manipulability properties for the three-alternative model.