Guides · Antitrust

Common Impact and Pass-Through at Class Certification

In an antitrust damages class, certification usually turns on whether the plaintiffs can prove, with evidence common to the class, that the alleged conspiracy injured its members. Rule 23(b)(3) asks whether common questions "predominate over any questions affecting only individual members," and in a price-fixing case the answer usually comes from the plaintiffs' economist's regression and the defense economist's critique. This guide covers the appellate decisions that frame that contest and what each expert has to show.

Guide 3 of 4 · September 22, 2026 · 8 min read
On this page
  1. Comcast
  2. Rail Freight
  3. Olean
  4. Averaging
  5. Pass-through
  6. What to prepare

Comcast: the model must match the theory

Comcast Corp. v. Behrend, 569 U.S. 27 (2013), set the baseline. The district court had accepted only one of the plaintiffs' four theories of antitrust impact, but the plaintiffs' damages model measured the effect of all four together. The Supreme Court reversed certification. It held that "a model purporting to serve as evidence of damages in this class action must measure only those damages attributable to that theory." Id. at 35. "Calculations need not be exact," but the contrary rule would mean that "any method of measurement is acceptable so long as it can be applied classwide, no matter how arbitrary the measurements may be," which "would reduce Rule 23(b)(3)'s predominance requirement to a nullity." Id. at 35-36. Without another methodology, "Questions of individual damage calculations will inevitably overwhelm questions common to the class." Id. at 34.

Comcast also closed off a familiar deferral argument. The Court of Appeals had refused to consider attacks on the model "simply because those arguments would also be pertinent to the merits determination," and the Supreme Court held that this "ran afoul of our precedents requiring precisely that inquiry." Id. at 34.

For the plaintiffs' economist, the lesson is fit: the but-for world must reflect only the accepted theory of harm. For the defense economist, the first move is mapping: tie each benchmark, control and assumption to a theory of impact, and isolate whatever the model attributes to the violation that the surviving liability case cannot support.

Rail Freight: when the model itself finds uninjured members

The D.C. Circuit's railroad fuel surcharge litigation shows how a plaintiffs' model can supply the defense's best evidence. In the first appeal the court vacated certification and remanded for reconsideration under Comcast, stating that the regression was central to the plaintiffs' showing: "No damages model, no predominance, no class certification." In re Rail Freight Fuel Surcharge Antitrust Litig., 725 F.3d 244, 253 (D.C. Cir. 2013).

On remand, the plaintiffs' own damages model showed that 2,037 of 16,065 proposed class members, or 12.7 percent, had "only negative overcharges." In re Rail Freight Fuel Surcharge Antitrust Litig.-MDL No. 1869, 934 F.3d 619, 623-24 (D.C. Cir. 2019). The court affirmed the denial of certification: "even assuming the model can reliably show injury and causation for 87.3 percent of the class, that still leaves the plaintiffs with no common proof of those essential elements of liability for the remaining 12.7 percent." Id. at 624.

Three features of the opinion matter in practice. First, the court assumed without deciding that a de minimis exception exists, and it noted the district court's reading of prior cases that "5% to 6% constitutes the outer limits of a de minimis number." Id. at 625. Second, it stressed that the plaintiffs had proposed no "further way," short of individual trials, to separate the uninjured from the injured. Id. Third, it rejected two rescue arguments. Attributing the negative estimates to prediction error only described a weakness in the plaintiffs' own evidence; it was not common proof that those shippers were injured. Id. at 624. And the fact that the uninjured shippers accounted for a small share of revenue did not help, because "revenue is irrelevant to predominance, which looks to whether elements such as causation and injury may be proved through common evidence, not how much the defendants benefited from any wrongdoing." Id. at 626.

Olean: no per se rule, but the court must resolve the dispute

The Ninth Circuit, sitting en banc in Olean Wholesale Grocery Cooperative, Inc. v. Bumble Bee Foods LLC, 31 F.4th 651 (9th Cir. 2022) (en banc), took a different path in the packaged tuna litigation. It first held that "plaintiffs must prove the facts necessary to carry the burden of establishing that the prerequisites of Rule 23 are satisfied by a preponderance of the evidence." It then rejected the argument that Rule 23 forbids certifying a class that "potentially includes more than a de minimis number of uninjured class members." Id. at 669. Instead, "When individualized questions relate to the injury status of class members, Rule 23(b)(3) requires that the court determine whether individualized inquiries about such matters would predominate over common questions." The majority read Rail Freight as a fact-bound application of that test rather than a numerical rule.

The case turned on a 28 percent figure. The defense economist re-ran the plaintiffs' pooled regression purchaser by purchaser and found no positive, statistically significant overcharge for 169 of 604 direct purchasers. The majority held that this test did not establish that those purchasers were uninjured; it was "aimed at undermining confidence in" the pooled model, and "At most, this critique supports the more attenuated argument that [the] model is unreliable, or would be unpersuasive to a jury." Because the district court had considered and resolved that methodological dispute, certification stood. The dissent warned that the opportunity to remove uninjured members at trial "is a phantom solution because defendants will have little choice but to settle before then."

The national question remains open. The Supreme Court granted review of whether a damages class may include both injured and uninjured members, then dismissed the writ as improvidently granted. Laboratory Corp. of America Holdings v. Davis, 605 U.S. 327 (2025) (per curiam). Justice Kavanaugh, dissenting, would have held that "a federal court may not certify a damages class that includes both injured and uninjured members." Until the Court decides the issue, the forum's circuit law controls how a member-level count will be received.

Averaging and pooled regressions

The defense theme in most of these cases is that a single average overcharge hides variation. In Olean, the defendants argued that the model's "averaging assumptions" applied one uniform overcharge to every direct purchaser and "paper over" individualized negotiations. The en banc court rejected the categorical form of that attack: "any categorical argument that a pooled regression model cannot control for variables relating to the individualized differences among class members must be rejected." The relevant question "is whether each member of the class can rely on [the] model to show antitrust impact of any amount," and "A lack of persuasiveness is not fatal at certification." That standard tracks Tyson Foods, Inc. v. Bouaphakeo, 577 U.S. 442, 455 (2016), which asks whether "each class member could have relied on that sample to establish liability if he or she had brought an individual action."

What survives for the defense is specific, testable criticism. Olean described a Chow test as designed to "determine whether it is appropriate to pool potential subgroups when estimating the average effect of the alleged conspiracy," and it said courts must consider "unsupported assumptions, erroneous inputs, or nonsensical outputs such as false positives." The strongest defense showings identify subgroups for which the pooled estimate is not informative, or purchases the conduct could not have affected that the model nonetheless treats as overcharged, as with the legacy contracts at issue in Rail Freight.

Indirect purchasers and pass-through

Under federal antitrust law, "the overcharged direct purchaser, and not others in the chain of manufacture or distribution, is the party" injured for purposes of section 4 of the Clayton Act. Illinois Brick Co. v. Illinois, 431 U.S. 720, 729 (1977). Indirect purchaser classes therefore typically pursue damages under state law; in Rail Freight, the indirect purchasers sought injunctive relief under section 16 and raised state-law claims. 934 F.3d at 620-21. For these classes, common impact has two links: an overcharge to the direct purchaser, and pass-through of that overcharge down the chain to each class member.

Olean shows how courts treat the second link. For the end-payer class, the plaintiffs' expert estimated pass-through rates ranging from 65.3 to 135 percent, with an estimated 100 percent for the class as a whole, supported by retail scanner data and the defendants' records. For the commercial food preparer class, the defendants argued that the expert wrongly assumed every member faced the same overcharge and "the same pass-through rate." The court upheld the models, "provided that the district court considers factors that may undercut the model's reliability (such as unsupported assumptions, erroneous inputs, or nonsensical outputs such as false positives) and resolves disputes raised by the parties."

The defense pass-through attack works best when concrete: channels that absorbed the overcharge, retail price points that did not move, or aggregate estimates that cannot show each member paid more. The plaintiffs' economist should be ready to explain rates above 100 percent and to show pass-through by channel, not only on average.

What to prepare

  • Map every element of the damages model to the theory of impact the court has accepted.
  • Run the model member by member or by subgroup, and count zero, negative and insignificant estimates before the other side does.
  • If some members show no injury, propose a winnowing mechanism that does not require individual trials.
  • Test whether pooling is appropriate and document the result either way.
  • Search for false positives: overcharges on purchases the conduct could not have touched.
  • For indirect purchasers, prove pass-through at each link and by channel.
  • Know the forum: Rail Freight and Olean frame uninjured members differently, and the Supreme Court has not resolved the question.

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Sources

This guide is general information, not legal advice.

How each court of appeals applies amended Rule 702: see the Rule 702 tracker.

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Experts in this guide's practice

Cartel-overcharge damages economistPlaintiff common-impact economistIndirect-purchaser pass-through economistDefense class-certification antitrust economistMarket-definition economistExclusionary-conduct damages economistLabor-market antitrust economist

The series

01Securities · September 8, 2026Daubert Challenges to Event Studies in Securities Cases02Securities · September 15, 2026Price Impact at Class Certification After Goldman03Antitrust · September 22, 2026Common Impact and Pass-Through at Class Certification04Any expert · September 29, 2026Amended Rule 702 After Nearly Three Years: What Courts Exclude

Related: the expert class library, a complete sample brief, and how it works.