Market-efficiency expert
Expert class library · Securities · Plaintiff side
Tests whether a security traded in an efficient market so that investors may invoke the fraud-on-the-market presumption of reliance. Walks the court through the Cammer and Krogman factors and supports them with empirical cause-and-effect tests.
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Questions this testimony turns on
- Did the security trade in an efficient market throughout the class period?
- Do trading volume, analyst coverage, market makers, and S-3 eligibility support a finding of efficiency under Cammer?
- Does an event study show that the price reacted promptly to new, company-specific information?
- Do market capitalization, bid-ask spread, and public float point toward efficiency under Krogman?
Methods
- Cammer factor analysis
- Krogman factor analysis
- Cause-and-effect event tests
- Trading volume and analyst coverage review
How the testimony is attacked
- Event study designed to reach a result. Defendants argue the cause-and-effect study was built to confirm efficiency rather than test it. In Bell v. Ascendant Solutions the district court excluded the plaintiffs' expert on that ground, and without him the plaintiffs could not show efficiency.
- Results that depend on a single day. Opponents rerun the study without outlier dates to show the difference between news days and no-news days disappears. The Fifth Circuit noted that dropping one no-news day erased the statistically significant difference in the excluded study.
- Inconsistent or irreconcilable event studies. Defendants attack event studies that yield conflicting results across specifications. In Carpenters Pension Trust Fund v. Barclays the court held these criticisms went to weight, not admissibility, and denied the motion to exclude.
- Subjective selection of news events. Critics say the expert picked which news days to test using judgment rather than objective criteria. The Barclays court accepted that single-firm event studies often rely on subjective assessments, which affects weight rather than admissibility.
- Information efficiency versus fundamental value. Defendants sometimes argue the market did not price the security at fundamental value. In the Emergent BioSolutions case the court held that Basic requires only informational efficiency and found the expert's tests reliable.
What the public record shows
Courts have filed at least 5 opinions since 2015 that discuss this class of testimony and cite Daubert or Rule 702, as of October 4, 2026. 8 rulings that show how courts handle this class of testimony:
| Outcome | Case | Court | Year | Why |
|---|---|---|---|---|
| Exclusion reversed | Ohio Public Employees Retirement System v. Federal Home Loan Mortgage Corp.No. 25-3765 (6th Cir. Aug. 21, 2026) | 6th Cir. | 2026 | The Sixth Circuit vacated the exclusion of the plaintiffs' market-efficiency expert at class certification, holding that the exclusion rested on the trial court's rejection of a price-maintenance theory and its undue emphasis on the fifth Cammer factor, and that any legal conclusions in the report called for trimming rather than wholesale exclusion. |
| Admitted | City of Cape Coral Mun. Firefighters' Ret. Plan v. Emergent Biosolutions, Inc.322 F. Supp. 3d 676 | D. Md. | 2018 | The court rejected the defense argument, supported by a rebuttal expert, that the plaintiffs' efficiency tests were inadmissible, finding the event study and collective tests to be accepted and reliably applied methods. |
| Admitted | Angley v. UTi Worldwide Inc.311 F. Supp. 3d 1117 | C.D. Cal. | 2018 | The court accepted the plaintiff's market-efficiency expert, holding that the undisputed first four Cammer factors and the Krogman factors established efficiency and that, even if the fifth factor were required, her event study satisfied it despite the defense attack on it as unreliable and biased. |
| Admitted | Willis v. Big Lots, Inc.242 F. Supp. 3d 634 | S.D. Ohio | 2017 | In certifying the class, the court relied on its separate order denying the defendants' Daubert motion and accepted the plaintiffs' event study as proof of the fifth Cammer factor, rejecting arguments that it lacked an ex ante hypothesis and was biased by including corrective disclosure dates. |
| Admitted | Waggoner v. Barclays PLC875 F.3d 79 | 2d Cir. | 2017 | Affirming class certification, the Second Circuit held the district court acted within its discretion in finding an efficient market from the unchallenged indirect Cammer and Krogman factors without relying on the plaintiffs' event study, and that defendants seeking to rebut the Basic presumption must do so by a preponderance of the evidence. |
| Admitted | Carpenters Pension Trust Fund v. Barclays PLC310 F.R.D. 69 | S.D.N.Y. | 2015 | The court denied the defendants' Daubert motion against the plaintiffs' efficiency expert, holding that attacks on his event studies went to weight and that the fifth Cammer factor is not dispositive. |
| Admitted | McIntire v. China MediaExpress Holdings, Inc.38 F. Supp. 3d 415 | S.D.N.Y. | 2014 | Ruling on a Daubert motion at class certification, the court held the plaintiffs' efficiency expert qualified and found her news-day versus non-news-day event study sufficiently reliable, treating the auditor's remaining criticisms as matters of weight for the Cammer analysis. |
| Excluded | Bell v. Ascendant Solutions, Inc.422 F.3d 307 | 5th Cir. | 2005 | The district court excluded the plaintiffs' market-efficiency expert because his event study was unreliable and seemingly designed to support efficiency, and the Fifth Circuit affirmed the denial of class certification because the plaintiffs had no other serious showing of efficiency. |
Each case links to the free opinion text on CourtListener.
In federal court: amended Rule 702
In federal court, 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
- Defense event-study econometrician
- Plaintiff event-study and loss-causation econometrician
- Securities accounting and GAAP expert
Guides
- Daubert Challenges to Event Studies in Securities Cases
- Price Impact at Class Certification After Goldman
- Amended Rule 702 After Nearly Three Years: What Courts Exclude
- Market Efficiency at Class Certification: Cammer and Krogman
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Updated October 4, 2026. How this page is built: rulings are found by searching court opinions on CourtListener. The summaries are written by AI working from the full text of each opinion, and every citation and link is checked automatically. 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. Spotted an error? Tell us.