Expert evidence commonly plays an important role in class certification determinations.  On August 5, the Seventh Circuit addressed this issue, holding that in a proposed antitrust class action, the district court erred in certifying a class when it failed to engage with conflicting expert evidence regarding antitrust impact that could have established lack of predominance.        

The case, Arandell Corp. v. Xcel Energy Inc., — F.4th —, 2025 WL 2218111 (7th Cir. 2025) was a long-running natural gas price fixing case.  Plaintiffs moved to certify a Rule 23(b)(3) class.  They argued that common questions of law or fact predominated, including “whether the class paid higher prices for natural gas[.]”  Id. at *4.  Plaintiffs and defendants had competing experts on the predominance issue as it related to impact.  Id. 

The district court certified the class.  In doing so, the court ruled that plaintiffs’ experts’ “opinions are admissible” but determined that did “not mean plaintiffs have established the existence of a common method of proof.”  Id. at *5 (emphasis in original).  Despite this determination about plaintiffs’ experts’ opinions, the court did not “expressly address or make findings about the defense arguments that the plaintiffs’ models were inadequate so as to defeat predominance.”  Id. 

The Seventh Circuit reversed.  It held that, in performing the “rigorous analysis” required by Rule 23, district courts must resolve disputed expert issues bearing on predominance.  In other words, “where the defendants have offered admissible evidence that, if credited, would mean that individual questions would predominate over common questions,” the court “must investigate[] the realism of the expert evidence in light of the defendants’ counterarguments, and take evidence to that end.”  Id. at *7.  Courts need not—and indeed cannot—“resolve [expert] disputes on the merits unrelated to the decisions essential to Rule 23,” but those that do relate to class certification questions must be addressed.  Id.  The Seventh Circuit instructed the district court on remand to “engage with [the expert] debates and make findings of fact, ultimately, as to whether plaintiffs have shown the existence of a national market” in which defendants’ alleged price fixing impacted prices.  Id. at *8. 

Litigants should be mindful of Arandell’s requirement that the district court resolve contested expert issues bearing on issues like predominance before certifying a class.