Guides · Antitrust

How Often Courts Exclude Antitrust Economists, and Why

Antitrust cases are built on economics. Market definition, market power, antitrust injury, common impact at class certification and damages all usually require an economist, and each side has an obvious incentive to try to remove the other's before trial. Practitioners know that Daubert motions against antitrust economists are routine. Until recently there was little systematic evidence of how often they succeed. A working paper by Edoardo Peruzzi, an economist and philosopher of science, supplies some. This guide summarizes its findings, then turns to the rulings in the library that show why economists are excluded and what courts leave to the jury.

Guide 7 of 10 · October 19, 2026 · 7 min read
On this page
  1. The numbers
  2. Why plaintiffs'
  3. What gets excluded
  4. What goes to weight
  5. Admissible vs. enough
  6. What to prepare

The numbers

Peruzzi built a dataset of 286 Daubert challenges to economists in federal antitrust cases decided from 1993 to 2021. It covers more than 200 expert witnesses in 182 cases before 174 judges, limited to challenges that could be confidently attributed to Daubert and Rule 702. The main findings, as the author summarized them:

  • Over a third succeed. Economists' opinions were fully or partially excluded in 103 of the 286 challenges, or 36 percent. The remaining 183 were denied.
  • Challenges rose over time. Both challenges and exclusions increased, peaking at 34 challenges in 2017, and the increase was not explained by a matching rise in antitrust filings. The author reads this as strategic use of Daubert to end disputes early.
  • Antitrust draws more than its share. Using broader data on gatekeeping challenges to economists (including challenges under Rules 403 and 703 and at class certification), about 18 percent arose in antitrust cases, compared with about 12 percent in patent, trademark and copyright cases and about 6 percent in labor and employment. Antitrust is about 0.3 percent of federal civil cases; patent cases are about 4 percent.
  • Plaintiffs' experts are challenged more. Plaintiffs' economists faced about 71 percent of the challenges (203), and defense economists 29 percent (83).
  • Defense experts are excluded at a higher rate. Of the challenged plaintiffs' experts, 134 were admitted and 69 excluded, about 34 percent. Of the challenged defense experts, 49 were admitted and 34 excluded, about 41 percent. The author suggests plaintiffs may challenge more selectively, only where there is a clear deficiency.
  • Court-appointed experts are rare. Across the 286 challenges, a court-appointed expert was used only twice.

Two cautions apply. The dataset ends in 2021, before the December 2023 amendment to Rule 702, which emphasized that courts must find each reliability requirement met by a preponderance of the evidence. And partial exclusions are counted with full ones, so the 36 percent figure includes rulings that removed one opinion and left the expert's core analysis in place.

Why plaintiffs' experts draw most challenges

The asymmetry in challenges follows from the burden of proof. A plaintiff needs economic evidence to prove market definition, market power, impact and damages; if its economist is excluded, the case can fail before trial. A defendant can often win by undermining the plaintiff's proof without affirmative expert testimony. So defendants have more to gain from a successful challenge and file more of them.

What gets excluded

The library's rulings show recurring grounds.

No reliable comparison. In In re Aluminum Phosphide Antitrust Litigation (D. Kan. 1995), the court excluded a price-fixing damages expert who ignored pre-conspiracy data, ran no regression to account for supply, demand and other factors unrelated to the conspiracy, and rested his before-and-after comparison on unsupported assumptions.

Inputs the expert cannot explain. In ZF Meritor v. Eaton (3d Cir. 2012), the Third Circuit affirmed exclusion of a damages opinion in an exclusive dealing case because the but-for profits came from a summary business plan whose origin and assumptions the expert could not explain, though the plaintiffs were allowed to submit alternate calculations. Insight Equity v. Transitions Optical (D. Del. 2017) admitted a damages implementation built on detailed company projections, distinguishing the thin plan in ZF Meritor.

A market without facts. In It's My Party v. Live Nation (D. Md. 2015), the court excluded a venue market definition that rested on a histogram and anecdotes about artists preferring amphitheaters, because it did not show those artists would refuse to switch venues if prices rose, which is the question the hypothetical monopolist test asks.

Models that contradict each other or the class. In In re LIBOR-Based Financial Instruments Antitrust Litigation (S.D.N.Y. 2018), the court excluded a plaintiffs' economist's class-wide opinions because his many models were internally inconsistent and inconsistent with a co-expert's. In Kamakahi v. American Society for Reproductive Medicine (N.D. Cal. 2015), regressions on capped egg donor compensation were excluded at class certification because the three agencies studied showed sharply different effects and were not representative of the class.

Defense opinions that answer the wrong legal question. Consistent with the higher exclusion rate for defense experts, defense economists lose most often when they stray from economics into legal standards. In In re Delta/AirTran Baggage Fee Antitrust Litigation (N.D. Ga. 2016), the court excluded four defense experts' opinions that base fare reductions offset the challenged bag fee, holding that offsetting benefits cannot reduce price-fixing damages or defeat impact. A later ruling in the same case excluded one defense economist's views on what antitrust policy should allow and another's economic definition of collusion framed as preconditions to liability. In In re Mushroom Direct Purchaser Antitrust Litigation (E.D. Pa. 2016), a defense report was excluded to the extent it opined on whether the class should be certified.

What goes to weight

The majority of challenges fail, and the rulings explain why. Courts treat the standard tools as reliable and leave disputes about data and specification to cross-examination. In In re Scrap Metal Antitrust Litigation (6th Cir. 2008), the Sixth Circuit affirmed admission of an overcharge analysis despite complaints about the accuracy of the price index data. In In re Processed Egg Products Antitrust Litigation (E.D. Pa. 2015), odd results in data subsets did not make a regression estimating a single average overcharge unreliable as a whole. In Dial Corp. v. News Corp. (S.D.N.Y. 2016), disputes over the plaintiffs' economist's critical loss analysis and benchmark margins went to weight. Appellate courts also reverse exclusions: in Teradata v. SAP (9th Cir. 2024), the Ninth Circuit held that excluding a tied-market definition was an abuse of discretion, because an aggregate diversion ratio built from customer data is an accepted way to implement the hypothetical monopolist test.

Admissible is not the same as sufficient

At class certification, surviving Daubert does not end the inquiry. In In re Rail Freight Fuel Surcharge Antitrust Litigation (D.C. Cir. 2019), the plaintiffs' regression models were found reliable enough to admit, but the D.C. Circuit upheld denial of certification because problems such as false positives for shippers who could not have been injured undermined the model as common proof. The defense economists' work identifying those shippers was itself admitted because it was built on the plaintiffs' own data and model. In Olean Wholesale Grocery Cooperative v. Bumble Bee Foods (9th Cir. 2022) (en banc), no Daubert challenge was raised, and the court affirmed certification after the district court weighed the defense critique of the pooled regression rather than merely asking whether it was admissible. The economist's fight often continues past the motion to exclude.

What to prepare

  • Expect a challenge, especially to a plaintiff's economist, and build the record for it from the first report.
  • Ground the benchmark, the but-for world and the market definition in documented facts the expert can explain.
  • Run the robustness checks that respond to predictable critiques, and keep multiple models consistent with each other and with co-experts.
  • Keep defense opinions within economics; do not opine on legal standards or on whether a class should be certified.
  • At class certification, test the model as common proof, not just as admissible evidence.
  • Remember that a third of challenges succeed at least in part, and that partial exclusion of one opinion can still change the case.

The library's antitrust practice page lists the economist classes and the rulings behind them.

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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 economistDefense cartel econometrician

The series

10Mass tort · October 20, 2026General Causation in Mass Torts: Bradford Hill Under Rule 70209Securities · October 19, 2026Section 11 Damages and Negative Causation08Antitrust · October 19, 2026Overcharge Regressions in Price-Fixing Cases07Antitrust · October 19, 2026How Often Courts Exclude Antitrust Economists, and Why06Securities · October 13, 2026Loss Causation, Damages and the Inflation Ribbon05Securities · October 6, 2026Market Efficiency at Class Certification: Cammer and Krogman04Any expert · September 29, 2026Amended Rule 702 After Nearly Three Years: What Courts Exclude03Antitrust · September 22, 2026Common Impact and Pass-Through at Class Certification02Securities · September 15, 2026Price Impact at Class Certification After Goldman01Securities · September 8, 2026Daubert Challenges to Event Studies in Securities Cases

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