Egalitarianism in Mechanism Design∗ Geoffroy de Clippely This Version: January 2012 Abstract This paper examines ways to extend egalitarian notions of fairness to mechanism design. It is shown that the classic properties of con- strained efficiency and monotonicity with respect to feasible options become incompatible, even in quasi-linear settings. An interim egali- tarian criterion is defined and axiomatically characterized. It is applied to find \fair outcomes" in classical examples of mechanism design, such as cost sharing and bilateral trade. Combined with ex-ante utilitari- anism, the criterion characterizes Harsanyi and Selten's (1972) interim Nash product. Two alternative egalitarian criteria are proposed to il- lustrate how incomplete information creates room for debate as to what is socially desirable. ∗The paper beneficiated from insightful comments from Kfir Eliaz, Klaus Nehring, David Perez-Castrillo, Kareen Rozen, and David Wettstein. Financial support from the National Science Foundation (grant SES-0851210) is gratefully acknowledged. yDepartment of Economics, Brown University. Email:
[email protected] 1. INTRODUCTION Developments in the theory of mechanism design, since its origin in the sev- enties, have greatly improved our understanding of what is feasible in envi- ronments involving agents that hold private information. Yet little effort has been devoted to the discussion of socially desirable selection criteria, and the computation of incentive compatible mechanisms meeting those criteria in ap- plications. In other words, extending the theory of social choice so as to make it applicable in mechanism design remains a challenging topic to be studied. The present paper makes some progress in that direction, with a focus on the egalitarian principle.