When a plaintiff seeking to certify a class relies on an expert to establish that classwide issues predominate, must the expert testimony satisfy the requirements for admissibility, or does some lesser or variable standard apply?

QUESTION PRESENTED In Comcast Corp. v. Behrend, this Court held that plaintiffs must present “evidentiary proof” to satisfy Rule 23, but it did not reach the question on which review was initially granted: whether such evidence, including expert testimony, must be admissible. 569 U.S. 27, 32 n.4 (2013). Since Comcast, circuit courts have deepened a split on that question. The First, Third, Fifth, Seventh, and Eleventh Circuits require admissible evidence to support class certification. The Sixth, Eighth, and Ninth Circuits, by contrast, do not. The decision below entrenched the Ninth Circuit’s position on the short side of that split. Plaintiffs moved for class certification after the close of fact and expert discovery, alleging that an expert’s model would provide common proof needed to satisfy Rule 23’s predominance requirement. Although the expert proffered that he could develop a model to assess classwide injury, he had not yet even collected the data to do so, and he could not say what the model would show if he ever collected the needed data and ran it. The district court certified the class, and the Ninth Circuit affirmed, reasoning that evidence that supports a decision to certify a class under Rule 23 need not be admissible, and whether a court conducts a “full” or “limited” Daubert inquiry depends on whether an expert chooses to fully develop the model. The question presented is: When a plaintiff seeking to certify a class relies on an expert to establish that classwide issues predominate, must the expert testimony satisfy the requirements for admissibility, or does some lesser or variable standard apply?