No Evading Daubert at Class Certification Stage, Sixth Circuit Rules

An important issue in class action practice is how courts are to evaluate the reliability of expert evidence that purports to support class certification. On November 22, the Sixth Circuit joined a majority of circuits in holding that a full Daubert analysis is required at the class certification stage where the expert evidence is material to class certification.

In In re Nissan North Am., Inc. Litig., - F.4th -, 2024 WL 4864339 (6th Cir. Nov. 22, 2024), Nissan owners brought state law claims alleging various defects with automatic braking systems in Nissan vehicles. The district court certified 10 statewide classes under Fed. R. Civ. P. 23(b)(3). Id. at *1. On interlocutory appeal, the Sixth Circuit reviewed three aspects of the district court's certification decision: (1) whether the case involved common questions of law or fact under Rule 23(a)(1); (2) whether common questions predominated over individual ones under Rule 23(b)(3); and (3) whether the court could rely on expert evidence without ensuring that it satisfied the Daubert standard. Id. at *3. While it found error in the district court's determinations on each of these issues, this post focuses on the expert-related question.

The key expert-related question the Sixth Circuit considered is: "When challenged expert testimony is relevant to class certification, must a district court perform a Daubert analysis of the evidence?" Id. at *8. Joining the Third, Fifth, Seventh, and Eleventh Circuits, the Sixth Circuit held that "[i]f challenged expert testimony is material to a class certification motion, the district court must demonstrate the expert's credibility under Daubert." Id. at *9. (The Eighth and Ninth Circuits require a more limited Daubert analysis.) The Court grounded its holding in the Supreme Court's admonition that a class proponent must provide "evidentiary proof" that he satisfies Rule 23's requirements. Id. Unreliable expert testimony, the Sixth Circuit reasoned, cannot provide such "evidentiary proof." Id. Turning to the challenged expert opinion, the Court determined that it "is a critical piece of plaintiffs' effort to answer th[e] commonality inquiry" about whether Nissan vehicles suffered from the same type of brake defect. Id. Because the district court failed to assess this opinion under Daubert, the Court reversed and remanded.

The Nissan decision will likely raise additional questions in future cases about whether an expert opinion is "material" to class certification. In any event, the case illustrates the importance of understanding each Circuit's standard for expert testimony at class certification.