The “ascertainability” requirement for class certification is a crucial safeguard for both defendants and absent class members. There is some debate about its origin: some courts have held that it is implicit in Rule 23 that class members must be readily identifiable; others find ascertainability to be rooted in Rule 23(a)(1)’s numerosity mandate or Rule 23(b)(3)’s requirement that a class action be superior to other methods for resolving the controversy. Either way, courts agree that a class is ascertainable only if the class definition is sufficiently definite to make it administratively feasible for the court to determine by reference to objective criteria whether a particular person is a member of the putative class.
In two recent opinions—Hayes v. Wal-Mart Stores, Inc. (pdf), 2013 WL 3957757 (3d Cir. Aug. 2, 2013), and Carrera v. Bayer Corp., 2013 WL 4437225 (3d Cir. Aug. 21, 2013)—the Third Circuit vacated class certification orders because the plaintiffs hadn’t met their burden of proving that class members were ascertainable. These decisions are a goldmine for class action defendants: They provide great examples of the ascertainability requirement in action.