  We consider randomized mechanisms with optional participation. Preferences
over lotteries are modeled using skew-symmetric bilinear (SSB) utility
functions, a generalization of classic von Neumann-Morgenstern utility
functions. We show that every welfare-maximizing mechanism entices
participation and that the converse holds under additional assumptions. Two
important corollaries of our results are characterizations of an attractive
randomized voting rule that satisfies Condorcet-consistency and entices
participation. This stands in contrast to a well-known result by Moulin (1988),
who proves that no deterministic voting rule can satisfy both properties
simultaneously.
