The Third Circuit recently joined the Seventh, Eighth, and Ninth Circuits in holding that, where a Daubert challenge is made to the use of expert testimony in support of class certification, the Daubert challenge must be resolved at that stage. The Third Circuit 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.” In re Blood Reagents Antitrust Litigation, No. 12-4067, 2015 U.S. App. LEXIS 5630, *9 (3d Cir. Apr. 8, 2015).

That result is hardly surprising. What I found most useful in this opinion was a footnote stressing that “[l]ike any evidence, admissible expert opinion may persuade its audience, or it may not,” and “[w]eighing conflicting expert testimony at the certification stage is not only permissible; it may be integral to the rigorous analysis Rule 23 demands.” Id. at *12 n.10. If the plaintiff’s expert testimony at class certification is weak enough that whether it is admissible under Daubert is a close call, the district court might not even need to reach that issue. That is because the testimony is not persuasive enough to warrant class certification regardless of whether it meets the Daubert threshold. Courts may find that to be a less cumbersome way of resolving the issue, particularly given that class certification is decided by the court, not a jury, and Daubert is more important in the jury context.