Where class certification is based on allegations that a defendant's policy or practice has injured class members, what constitutes 'significant proof' that such policy or practice applies uniformly to all members of the class as required to establish commonality under Federal Rule of Civil Procedure 23(a)(2)?

QUESTION PRESENTED Federal Rule of Civil Procedure 23 provides that a district court may certify a class action “only if,” among other requirements, “there are questions of law or fact common to the class.” Fed. R. Civ. P. 23(a)(2). In the decision below, the District of Columbia Circuit deepened a circuit split that has emerged post-WalMart Stores, Inc. v. Dukes, 564 U.S. 338, 348, 350-51 (2011), as to what constitutes the “significant proof” necessary to establish the uniformity of an alleged policy or practice under Rule 23(a)(2). The question presented is: Where class certification is based on allegations that a defendant’s policy or practice has injured class members, what constitutes “significant proof’ that such policy or practice applies uniformly to all members of the class as required to establish commonality under Federal Rule of Civil Procedure 23(a)(2)?