Information invariance in variable-population social-choice problems

We examine the possibilities of extending Sen's taxonomy of fixed-populatio n information assumptions regarding the measurability and interpersonal com parability of individual utilities to social-choice problems where the popu lation may vary. It is shown that in order to avoid impossibility results, informationally more demanding assumptions than in the fixed-population fra mework are required. We provide characterizations of variable-population so cial-welfare orderings based on information assumptions, and we suggest a w ay of generating the required informational environment by means of norms t hat impose a domain restriction on the set of possible utility profiles.