Characterizing Welfare-egalitarian Mechanisms with Solidarity When Valuations are Private Information

In the problem of assigning indivisible goods and monetary transfers, we characterize welfare-egalitarian mechanisms (that are decision-efficient and incentive compatible) with an axiom of solidarity under preference changes and a fair ranking axiom of order preservation. This result is in line with characterizations of egalitarian rules with solidarity in other economic models. We also show that we can replace order-preservation with egalitarian-equivalence or no-envy (on the subadditive domain) and still characterize the welfare-egalitarian class. We show that, in the model we consider, the welfare-egalitarian mechanisms appear to be the best candidates to satisfy several different fairness and solidarity requirements as well as generating bounded deficits.