Independence of irrelevant interpersonal comparisons

Arrow’s independence of irrelevant alternatives (IIA) condition makes social choice depend only on personal rather than interpersonal comparisons of relevant social states, and so leads to dictatorship. Instead, a new “independence of irrele-vant interpersonal comparisons ” (IIIC) condition allows anonymous Paretian social welfare functionals such as maximin and Sen’s “leximin, ” even with an unrestricted preference domain. But when probability mixtures of social states are considered, even IIIC may not allow escape from Arrow’s impossibility theorem for individuals’ (ex-ante) expected utilities. Modifying IIIC to permit dependence on interpersonal comparisons of relevant probability mixtures allows Vickrey-Harsanyi utilitarian-ism