To a practitioner in the field of economic analysis and econometrics, the most interesting part of the Supreme Court’s decision, and the part with the most impact on expert testimony, in Wal-Mart v. Dukes is the recognition of the plaintiffs’ failure to satisfy Rule 23(a)(2)—the requirement that states the party seeking class certification must demonstrate that the members of the class have common questions of law or fact. Although the statistical and economic approach proffered by the plaintiffs’ experts was similar to that in other cases that had been certified, the Dukes decision highlighted a fundamental disconnect between the plaintiffs’ theory of the case and the expert evidence they used to support it. The gap is the difference between presenting an analysis with conclusions that are consistent with a common question of law or fact and presenting an analysis that is evidence of a common question. The Court’s statement regarding the requirement for satisfying Rule 23(a) is as follows:
Rule 23 does not set forth a mere pleading standard. A party seeking class certification must affirmatively demonstrate his compliance with the Rule—that is, he must be prepared to prove that there are in fact sufficiently numerous parties, common questions of law or fact, etc.
Wal-Mart Stores, Inc. v. Dukes, 131 S. Ct. 2541 (2011) (emphasis added)