Listen Up Class: The Role of Daubert at the Class Certification Stage in the Ninth Circuit


Class certification is the feature fight of any putative class action lawsuit. If granted, it can multiply the stakes of a case several hundred- or thousand-fold. If denied, it can signal the end of the litigation. Because of its importance, parties often invest heavily in the class certification fight, including by offering – and challenging – expert testimony.

As this trend has become more common, more focus has been devoted to answering a key question – to what extent should Rule 702 apply at this critical juncture? A number of circuits have held that Rule 702 applies in full force and that opinions deemed inadmissible under Rule 702 should not be considered in regard to class certification; others, such as the Ninth Circuit, have taken a somewhat different approach. Recently, the Southern District of California, in Stewart v. Quest Diagnostics Clinical Labs., Inc., 2022 WL 5236821 (S.D. Cal. Oct. 5, 2022), weighed in on this question.

In Stewart, plaintiff moved for class certification alleging various employment claims against her former employer, defendant Quest Diagnostics. In support of her motion, plaintiff disclosed the opinions of an economics expert and a survey expert. The defendant opposed certification and moved to strike the opinions of both experts on various Daubert grounds.

In considering defendant’s motions to strike, the court applied Sali v. Corona Regional Medical Center, 909 F.3d 996 (9th Cir. 2018). In Sali, the Ninth Circuit held that, while the Daubert standard of admissibility does apply at the class certification stage, “an inquiry into the evidence’s ultimate admissibility should go to the weight that evidence is given at the class certification stage” and does not necessarily determine whether the evidence is considered at all. Id. at 1006. In other words, in the Ninth Circuit, it is the district court’s job to “evaluate the admissibility of the . . . [challenged opinions] under Daubert” and then, armed with the results of that analysis, “examine whether the expert declarations ‘tend[ ] to support class certification.’” Stewart, 2022 WL 5236821 at *7 (quoting Sali, 909 F.3d at 1006).

As a preliminary matter, the court rejected Stewart’s argument that, under Sali, it should not consider defendant’s motions to strike at the class certification stage. While Sali held that an expert declaration should not be disregarded at the class certification stage solely because of its inadmissibility, the court made clear that it was authorized to analyze expert declarations under Daubert and consider the results of that analysis as part of its class certification decision.

Ultimately, the Stewart court denied defendant’s motions to strike and granted in part the motion for class certification. In particular, as to the motions to strike, the court found that multiple of defendant’s arguments went to the weight of the evidence at class certification, not its admissibility. For example, the defendant challenged the plaintiffs’ survey expert’s opinions regarding a proposed survey of its employees that had not yet been conducted, contending such evidence was useless and speculative. Though the court notably did not hold that the proposed survey satisfied Rule 702, it nevertheless declined to strike the expert’s opinions, observing the expert’s proposed survey was still relevant to the class certification decision.

As to other arguments, the court found that they either related to issues not relevant to the class certification question, or otherwise did not justify exclusion at the class certification stage. After considering and denying defendant’s motions to strike, the court granted in part and denied in part the plaintiff’s class certification motion.

Whether, and how, a court considers the admissibility of scientific expert testimony at the class certification stage varies among federal circuits. While the Ninth Circuit endorses the application of Rule 702 at class certification—an approach followed by the Southern District of California in Stewart—it limits it by holding that “inadmissibility alone is not a proper basis to reject evidence submitted in support of class certification.” Other circuits, such as the Fifth and Seventh, do require expert testimony to be admissible under Daubert at the class certification stage in order to be considered. See Messner v. Northshore Univ. Health Sys., 669 F.3d 802 (7th Cir. 2012); Prantil v. Arkema Inc., 986 F.3d 570 (5th Cir. 2021). As the Third Circuit has put it, expert testimony that is inadmissible under Rule 702 “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.”  In re Blood Reagents Antitrust Litig., 783 F.3d 183, 187 (3d Cir. 2015). As the U.S. Supreme Court has not yet resolved this key circuit split, it is imperative in class action cases for counsel to be aware of the circuit split, understand the standard of admissibility that will be applied at the class certification stage, if any, and plan accordingly.

The material contained in this communication is informational, general in nature and does not constitute legal advice. The material contained in this communication should not be relied upon or used without consulting a lawyer to consider your specific circumstances. This communication was published on the date specified and may not include any changes in the topics, laws, rules or regulations covered. Receipt of this communication does not establish an attorney-client relationship. In some jurisdictions, this communication may be considered attorney advertising.

About the Author: Erica K. Drew

Erica Drew is a Products Liability associate residing in our Indianapolis, Indiana, office. She defends pharmaceutical and medical device companies against claims involving allegations of strict liability, negligence, failure to warn or consumer protection act violations.

About the Author: Joe Winebrenner

Joe Winebrenner is a product liability defense attorney who defends individual, mass tort and class action litigation matters. Joe focuses on dispositive motion practice, including motions for summary judgment and Daubert motions to exclude expert testimony. He has also successfully defeated motions for class certification, and he has appeared at numerous trials on behalf of clients. Joe represents clients in various industries, including pharmaceuticals, medical devices, and consumer and construction products.

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