Criteria to compare mechanisms that partially satisfy a property: an axiomatic study

We study criteria that compare mechanisms according to a property (e.g., Pareto efficiency or stability) in the presence of multiple equilibria. The multiplicity of equilibria complicates such comparisons when some equilibria satisfy the property while others do not. We axiomatically characterize three criteria. The first criterion is intuitive and based on highly compelling axioms, but is also very incomplete and not very workable. The other two criteria extend the comparisons made by the first and are more workable. Our results reveal the additional robustness axiom characterizing each of these two criteria.