Third Circuit:

“[The district court] need not turn class certification into a mini-trial.... We understand the Court’s observation [i.e., the Supreme Court’s observation in Dukes] to require a district court to evaluate whether an expert is presenting a model which could evolve to become admissible evidence, and not requiring a district court to determine if a model is perfect at the certification stage.” (Behrend v. Comcast Corp., 655 F.3d 182 (3d Cir. 2011))

Seventh Circuit:

“When an expert’s report or testimony is ‘critical to class certification,’ ... [the] district court must make a conclusive ruling on any challenge to that expert’s qualifications or submissions before it may rule on a motion for class certification.... If a district court has doubts about whether an expert's opinions may be critical for a class certification decision, the court should make an explicit Daubert ruling” (Messner v. Northshore Univ. HealthSystem, 2012 U.S. App. LEXIS 731 (7th Cir. Jan. 13, 2012))

Eighth Circuit:

“[Defendant’s] desire for an exhaustive and conclusive Daubert inquiry before the completion of merits discovery cannot be reconciled with the inherently preliminary nature of pretrial evidentiary and class certification rulings.” (In re Zurn Pex Plumbing, 644 F.3d 604 (8th Cir. 2011))

Ninth Circuit:

“[T]he district court seems to have confused the Daubert standard [of admissibility] ... with the ‘rigorous analysis’ standard to be applied when analyzing commonality. Instead of judging the persuasiveness of the evidence presented, the district court seemed to end its analysis of the plaintiffs’ evidence after determining such evidence was merely admissible.” (Ellis v. Costco Wholesale Corp., 657 F.3d 970 (9th Cir. 2011))