Group Identification

Comments welcome. I study a model of group identification in which individuals ’ opinions as to the mem-bership of a group are aggregated to form a list of group members. Potential aggregation rules are studied through the axiomatic approach. I introduce two axioms, meet separa-bility and join separability, each of which requires the list of members generated by the aggregation rule to be independent of whether the question of membership in a group is separated into questions of membership in two other groups. I use these axioms to char-acterize a class of one-vote rules, in which one opinion determines whether an individual is considered to be a member of a group. I then show that the only anonymous one-vote rule is self-identification, in which each individual determines for himself whether he is a member of the group