Whether Rule 23 and due process require district courts to undertake a rigorous analysis to determine whether the plaintiff has established that class membership is ascertainable through an administratively feasible method before certifying a class?

QUESTION PRESENTED Three circuits have held that Rule 23(b)(3) requires proponents of class certification to show an administratively feasible method for identifying class members. Four held it does not. Among other things, the requirement ensures that i) putative class members can be identified without individualized minitrials that defeat the efficiencies of class actions, ii) persons without a claim are not included in the class, iii) class members can receive appropriate notice of their rights, and iv) defendants can enforce class judgments and settlement releases. In the case below, respondent did not propose an administratively feasible method to ascertain class membership. The undisputed record evidence established that no such method was possible. Yet the district court certified the class anyway because it assumed that the class would “likely” turn out to be ascertainable and petitioner could always move to decertify or redefine the class later if the class proceedings proved unworkable. Contrary to the ruling below, do Rule 23 and due process require district courts to undertake a rigorous analysis to determine whether the plaintiff has established that class membership is ascertainable through an administratively feasible method before certifying a class?