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.