Plaintiff common-impact economist
Expert class library · Antitrust · Plaintiff side
Shows at class certification that the alleged conduct injured all or nearly all class members using evidence common to the class. Pairs pricing-structure analysis with regression models that estimate impact across purchasers.
What this expert is retained to answer
- Can antitrust injury to all or nearly all class members be shown with common evidence?
- Does the market's pricing structure transmit an overcharge broadly across purchasers?
- Does the class-wide regression find injury only where injury was possible?
- Is the damages model consistent with the theory of liability, as Comcast requires?
Methods
- Pricing structure analysis
- Class-wide regression with impact dummies
- Price correlation tests
- Damages model consistent with liability theory
How the testimony is attacked
- False positives. Defendants test the model on purchasers who could not have been harmed and show it still finds overcharges. In Rail Freight that showing for legacy shippers defeated class certification even though the model was admissible.
- Uninjured class members hidden by averaging. Defendants argue a pooled regression masks individual variation and that a large share of the class suffered no injury. In Olean the defense expert's critique was weighed rigorously, and the en banc court left the remaining dispute for trial.
- Admissibility is not the same as Rule 23 reliability. Courts may admit a model under Rule 702 and still find it unable to prove class-wide impact. The D.C. Circuit in Rail Freight endorsed the district court's view that reliability under Rule 23 can demand more.
- Internally inconsistent models. A model that conflicts with itself or with a co-expert's work invites exclusion. In LIBOR the court excluded an economist whose multiple but-for models were inconsistent with each other and with another plaintiffs' expert.
- Correlation offered as causation. Showing that two prices move together does not establish that the conduct caused class members' losses. The LIBOR court excluded opinions that bridged that gap with correlation alone.
What the public record shows
A deliberately narrow CourtListener search, "common impact" AND regression AND antitrust AND (Daubert OR "Rule 702"), returned 12 opinions filed since 2015, as of October 2, 2026; broader searches return more. Three that show how courts handle this class of testimony:
| Outcome | Case | Court | Why |
|---|---|---|---|
| Admitted | Olean Wholesale Grocery Cooperative v. Bumble Bee Foods LLC31 F.4th 651 | 9th Cir. 2022 | The en banc Ninth Circuit affirmed class certification resting on the plaintiffs' expert's pooled regression, noting that no Daubert challenge was raised and that the trial court had rigorously considered the defense critique about uninjured purchasers. |
| Admitted | In re Rail Freight Fuel Surcharge Antitrust Litigation (MDL No. 1869)934 F.3d 619 | D.C. Cir. 2019 | The trial court found the plaintiffs' regression models reliable enough to admit, but the D.C. Circuit upheld denial of class certification because concerns such as false positives for shippers who could not have been injured undermined the model as common proof. |
| Excluded | In re Libor-Based Fin. Instruments Antitrust Litig.299 F. Supp. 3d 430 | S.D.N.Y. 2018 | At class certification the court excluded a plaintiffs' economist's opinions that class-wide methods could show manipulation and its impact, because his many models were internally inconsistent and inconsistent with a co-expert's opinions. |
Each case links to the free opinion text on CourtListener.
Under amended Rule 702
Since December 1, 2023, Rule 702 says expressly that the party offering an expert must show the court it is more likely than not that the testimony meets each requirement: that it rests on sufficient facts or data, uses reliable methods, and reflects a reliable application of those methods to the case. Questions about the basis of an opinion are no longer automatically matters of weight for the jury. For how the circuits have applied the amendment, see the Rule 702 tracker, which follows each court of appeals; for what that means for preparing or attacking this class of expert, see the guide on amended Rule 702.
Related classes
- Cartel-overcharge damages economist
- Defense class-certification antitrust economist
- Indirect-purchaser pass-through economist
Guides
- Common Impact and Pass-Through at Class Certification
- Amended Rule 702 After Nearly Three Years: What Courts Exclude
Simulating this class on a matter
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Last reviewed October 2, 2026. How this page is built: rulings are found by searching court opinions on CourtListener, and each one is read in the opinion before it is summarised here; outcomes are labelled by what the court did with the expert's testimony. No individual expert is named. This page summarises public decisions for orientation and is not legal advice; read the opinion before relying on any ruling.