Evan M. Tager is a Partner with Mayer Brown LLP in the firm’s Washington, DC office and is the WLF Legal Pulse’s Featured Expert Contributor on Judicial Gatekeeping of Expert Evidence.


The federal courts of appeals have been divided as to whether district courts must apply a full-blown Daubert analysis when evaluating expert testimony offered in support of or opposition to class certification.

The Eighth and Ninth Circuits have held that district courts need not determine whether such expert testimony is admissible at trial under Daubert before relying on it to resolve class-certification issues.1

In contrast, the Seventh Circuit held more than a decade ago that “a district court must perform a full Daubert analysis before certifying the class if the situation warrants” and that failure to do so is an abuse of discretion.2  And the Third and Eleventh Circuits followed suit.3

In Prantil v. Arkema Inc., which was decided on January 22, the Fifth Circuit agreed with the Third, Seventh, and Eleventh Circuits.  (Disclosure:  I and colleagues at my firm represented Arkema in this case.)

Prantil is a putative environmental class action against chemical manufacturer Arkema Inc.  As a resulting of flooding from Hurricane Harvey, Arkema’s facility in Crosby, Texas lost power.  Chemicals that needed to be kept cool then combusted.  Local property owners and residents then brought a putative class action, seeking property damages, medical monitoring, and property remediation.

The district court certified a class of some 20,000 property owners and residents within a seven-mile radius of Arkema’s facility.  In the course of so doing, the district court relied heavily on the assertions of plaintiffs’ experts that they could establish injury and causation on a class-wide basis.  The Fifth Circuit granted review under Rule 23(f) and, after plenary briefing and oral argument, vacated the class certification order.

Although the court found several fatal flaws in the district court’s application of the Rule 23 factors, what warrants discussion here is its threshold ruling that the district court erred by not subjecting plaintiffs’ experts to full-blown Daubert scrutiny.

The Fifth Circuit held clearly and squarely that “the Daubert hurdle must be cleared when scientific evidence is relevant to the decision to certify.”  Quoting the Third Circuit with approval, the court explained that “[e]xpert testimony that is insufficiently reliable to satisfy the Daubert standard cannot ‘prove’ that the Rule 23(a) prerequisites have been met ‘in fact,’ nor can it establish ‘through evidentiary proof’ that Rule 23(b) is satisfied.”

The Fifth Circuit indicated that this conclusion was consistent with its case law holding that the “class certification inquiry . . . must be made based on adequate admissible evidence to justify class certification.”  It concluded that “if an expert’s opinion would not be admissible at trial, it should not pave the way for certifying a proposed class.”

The court went on to explain that the trial court had not, in fact, “appl[ied] Daubert’s reliability standard with full force.”  In particular, while the district court observed that one of the plaintiffs’ critical experts had failed to take into account background levels of the contaminants at issue, it indicated that doing so “was not necessary under Daubert at the class certification stage.”

The Fifth Circuit accordingly vacated the class-certification order and ordered the district court to both conduct a more searching Daubert inquiry and address the other flaws in the class-certification order identified by the panel.


  1. See Sali v. Corona Reg’l ’’Med. Ctr., 909 F.3d 996, 1006 (9th Cir. 2018); Zurn Pex Plumbing Prods. Liab. Litig., 644 F.3d 604, 611-12 (8th Cir. 2011).
  2. Am. Honda Motor Co. v. Allen, 600 F.3d 813, 816 (7th Cir. 2010).
  3. In re Blood Reagents Antitrust Litig., 783 F.3d 183, 187 (3d Cir 2015); Sher v. Raytheon Co., 419 F. App’x 887, 890 (11th Cir. 2011).