A characterization of unanimity with status quo: Fixed vs variable population

Abstract

This paper provides a characterization of a recent rule called the unanimity with status quo. The rule designates a specific alternative as the status quo, selecting it in all profiles except where another alternative is unanimously ranked first by all agents, in which case the unanimous alternative is chosen. Our characterization relies on the solidarity axiom of welfare dominance under preference replacement, in combination with unanimity and tops-only. The significance of this characterization lies in the demonstration of the axioms’ independence and the tightness of the characterization, meaning that weakening any axiom results in the emergence of additional rules. We also characterize the rule in the dynamic settings where new agents may enter the economy. Additionally, we examine the relationship between the two versions of solidarity axioms and the fairness axiom of anonymity.