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In Tyson Foods v. Bouaphakeo, a "donning and doffing" case brought under Iowa state law incorporating the Fair Labor Standards Act's overtime pay provisions, the petitioners asked the Supreme Court to reject the use of statistical evidence in Rule 23(b)(3) class certification. To its great credit, the Court refused. In its majority opinion, the Court cited both the Federal Rules of Evidence and federal common law interpreting the FLSA. In this paper, I take a moderately deep dive into the facts of the case, and the three opinions penned by Justice Kennedy (for the Court), Chief Justice Roberts (in concurrence), and Justice Thomas (in dissent) to explain why the case highlights the symbiotic relationship between Rule 23's certification-relevant provisions, underlying substantive law, and the Federal Rules of Evidence. I argue that the petitioners' attempts to forge a common law of statistical evidence for class certification was at war with core Federal Rules of Evidence and, consequently, with the Rules Enabling Act.

Along the way, I introduce the category of counterfactually relevant evidence. I show that the statistical and other representative evidence deployed by respondents fit in this category. I then explain why arguments against the use of this evidence--whether at trial or for other purposes such as class certification--must fail.

I close with a graphical depiction of how the three sources of positive law at issue in class certification--Rule 23, substantive law, and the Federal Rules of Evidence--interact with evidence used to prove that certification is warranted. The result is what I call the Triangle of Law, with each source of law occupying a vertex and the evidence at issue situated at the Triangle's center. This formulation should help scholars, practitioners, and courts focus attention on the independent but interconnected roles played by evidence and the three sources of law involved in class certification questions.


Federal Rules of Civil Procedure, FRCP, employment law, complex litigation, counterfactual evidence, class certification, Tyson Foods v. Bouaphakeo, Anderson v. Mt. Clemens Pottery Co., Wal-Mart Stores, Inc., v. Dukes, Mathews v. Eldridge

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University of Pennsylvania Law Review

Publication Citation

165 U. Pa. L. Rev. 1807 (2017)