Solidarity in preference aggregation: Improving on a status quo

Working in the Arrovian framework, we search for preference aggregation rules with desirable solidarity properties. In a fixed-population setting, we formulate two versions of the solidarity axiom welfare dominance under preference replacement. Although the stronger proves incompatible with efficiency, the combination of efficiency and our second version leads to an important class of rules which improve upon a “status quo” order. These rules are also strategy-proof, which reveals a further connection between solidarity and incentive properties. Allowing the population to vary, we again characterize the status quo rules by efficiency and a different solidarity axiom, population monotonicity. This extends a similar characterization of a subclass of these rules by Bossert and Sprumont (2014).