Defense event-study econometrician

Expert class library · Securities · Defense side

Uses event studies to test whether alleged misstatements or corrective disclosures actually moved the stock price. Retained to rebut price impact at class certification and to challenge loss causation and damages at summary judgment and trial.

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Questions this testimony turns on

Did the alleged misstatements or corrective disclosures cause a statistically significant stock price reaction?
Can the defendant rebut the presumption of class-wide reliance by showing the alleged fraud had no price impact?
How much of a price decline is explained by market, industry, or other non-fraud news?
Is the plaintiffs' event study, and the damages model built on it, reliable and consistent with the liability theory?

Methods

Market-model event study
Price impact rebuttal
Multiple-comparison adjustments
Confounding news analysis
Intraday price analysis

How the testimony is attacked

Inadequate control for industry movements. Plaintiffs argue the defense market model uses the wrong or too few indices, so returns that look normal would be abnormal against a better peer index. In the Halliburton remand the plaintiffs' expert claimed a peer index sharply improved the model's explanatory power.
Multiple-comparison adjustments that hide real price reactions. When the defense adjusts significance thresholds for testing many dates, plaintiffs say the correction is too conservative and produces false negatives. The Halliburton court accepted that an adjustment was warranted but applied the less conservative Holm-Bonferroni version instead of the Bonferroni version the defense expert used.
No price movement does not mean no price impact. Plaintiffs respond that a misstatement can maintain an already inflated price, so the absence of a price increase on the statement date proves little. In Goldman the district court repeatedly credited that inflation-maintenance theory before the Second Circuit reversed on other grounds.
Failure to isolate the event being studied. Opponents argue an event study that does not separate the challenged event from simultaneous news is misleading. In the Fannie Mae and Freddie Mac litigation the court admitted a defense event study because the expert never claimed it isolated one part of the challenged amendment from the rest.
Opinions that go beyond the event study. Courts examine each opinion separately, and a defense economist's add-on opinions can be excluded even when the event study survives. In the same Fannie Mae and Freddie Mac ruling the court excluded the expert's separate opinion on how a hypothetical commitment fee would have been set.
No front-end price impact. Defendants rebut the Basic presumption with event studies showing the stock did not move when the challenged statement was made. In IBEW Local 98 v. Best Buy the Eighth Circuit reversed class certification on that showing, and Goldman Sachs v. Arkansas Teacher requires courts to weigh the generic nature of statements as evidence of no price impact.

What the public record shows

Courts have filed at least 9 opinions since 2015 that discuss this class of testimony and cite Daubert or Rule 702, as of October 4, 2026. 7 rulings that show how courts handle this class of testimony:

Outcome	Case	Court	Year	Why
Admitted	Si v. Bed Bath & Beyond Corp.No. 1:22-cv-02541	D.D.C.	2024	The court denied class certification in a short-squeeze case, crediting the defense expert's event study, which used a shorter estimation window suited to the extreme volatility and found no statistically significant price reaction to the challenged statement, over the plaintiff's study using a 120-day window.
Admitted	Ark. Tchr. Ret. Sys. v. Goldman Sachs Grp., Inc.77 F.4th 74	2d Cir.	2023	The defense experts' event studies, including evidence that dozens of earlier reports about the same conflicts did not move the stock, were part of the record on which the Second Circuit reversed class certification for lack of price impact given the mismatch between generic statements and specific corrective disclosures.
Limited	In re Fannie Mae/Freddie Mac Senior Preferred Stock Purchase Agreement Class Action LitigationsMisc. No. 2013-1288 (D.D.C. Oct. 21, 2022)	D.D.C.	2022	The court admitted the defense expert's bond-yield event study because he did not claim it isolated one provision of the challenged amendment, but excluded his separate opinion on how a hypothetical commitment fee would have been set.
Sent back for review	Goldman Sachs Group, Inc. v. Arkansas Teacher Retirement System594 U.S. 113	U.S.	2021	The Supreme Court held that the generic nature of an alleged misrepresentation is often important evidence of price impact that courts must consider at class certification, even though it overlaps with materiality, and that defendants bear the burden of proving a lack of price impact by a preponderance of the evidence; it vacated and remanded.
Sent back for review	Carpenters Pension Trust Fund v. Allstate Corp.966 F.3d 595	7th Cir.	2020	The Seventh Circuit vacated class certification because the district court admitted the defense expert's opinion that the alleged misrepresentations had no price impact but declined to engage with it as too close to the merits, and remanded for the court to weigh that evidence.
Admitted	IBEW Local 98 Pension Fund v. Best Buy Co.818 F.3d 775	8th Cir.	2016	The Eighth Circuit reversed class certification, holding that the defense expert's event study, which showed the stock moved on an earlier press release and not on the later conference call statements at issue, was overwhelming evidence of no front-end price impact that rebutted the Basic presumption.
Admitted	Erica P. John Fund, Inc. v. Halliburton Co.309 F.R.D. 251	N.D. Tex.	2015	On remand from the Supreme Court, the court credited the defense expert's event study showing no price impact for all but one alleged corrective disclosure, and agreed a multiple-comparison adjustment was proper while substituting the Holm-Bonferroni method for the expert's Bonferroni method.

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.

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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.