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Loss Causation, Damages and the Inflation Ribbon

Class certification decides whether a securities case proceeds as a class; loss causation and damages decide what it is worth. Since Dura Pharmaceuticals, Inc. v. Broudo, plaintiffs must connect their losses to the revelation of the truth, not merely to an inflated purchase price, and their damages expert must separate the fraud from everything else that moved the stock. That work is expressed in the inflation ribbon, a day-by-day estimate of how much of the price was attributable to the misstatements. This guide covers the Dura requirement, disaggregation, the ribbon and its carry-back method, and how the defense attacks the model.

Guide 6 of 6 · October 13, 2026 · 8 min read
On this page
  1. Dura and the loss
  2. Disaggregating
  3. Building the
  4. Constant-dollar
  5. Damages models at
  6. How defense experts
  7. What to prepare

Dura and the loss causation requirement

In Dura, the Ninth Circuit had held that plaintiffs need only prove that the price on the date of purchase was inflated. The Supreme Court disagreed: "Normally, in cases such as this one (i.e., fraud-on-the-market cases), an inflated purchase price will not itself constitute or proximately cause the relevant economic loss." The Court gave two reasons. First, "at the moment the transaction takes place, the plaintiff has suffered no loss; the inflated purchase payment is offset by ownership of a share that at that instant possesses equivalent value." Second, a later lower price "may reflect, not the earlier misrepresentation, but changed economic circumstances, changed investor expectations, new industry-specific or firm-specific facts, conditions, or other events, which taken separately or together account for some or all of that lower price."

The Court's summary has framed every damages dispute since: "To 'touch upon' a loss is not to cause a loss, and it is the latter that the law requires." A contrary rule, the Court warned, "would tend to transform a private securities action into a partial downside insurance policy."

Plaintiffs therefore need an identifiable mechanism by which the truth reached the market, and a damages model that measures only the decline that revelation caused.

Disaggregating confounding information

A regression against market and industry indices removes sector-wide movements. It does not remove company news unrelated to the fraud, and that residual is where most loss causation fights are decided.

The Seventh Circuit's decision in Glickenhaus & Co. v. Household International, Inc. is the leading treatment. The jury had adopted a leakage model that, the court explained, "assumes that any changes in Household's stock price," other than those explained by market and industry trends, "are attributable to the fraud-related disclosures." The court identified the flaw: "If during the relevant period there was significant negative information about Household unrelated to these corrective disclosures (and not attributable to market or industry trends), then the model would overstate the effect of the disclosures and in turn of the false statements."

The court rejected both a requirement that the model "perfectly exclude" such factors and acceptance of a conclusory opinion. It set a burden-shifting middle ground: "If the plaintiffs' expert testifies that no firm-specific, nonfraud related information contributed to the decline in stock price during the relevant time period and explains in nonconclusory terms the basis for this opinion, then it's reasonable to expect the defendants to shoulder the burden of identifying some significant, firm-specific, non-fraud related information that could have affected the stock price." If the defense does so, the plaintiffs must account for it, for example by excluding those days from the model. On a record containing only a general statement that confounding news was insignificant, the court held: "That's not enough. A new trial is warranted on the loss-causation issue."

The Tenth Circuit's decision in In re Williams Securities Litigation shows the failure mode. The plaintiffs' expert offered a leakage scenario in which corrective disclosures occurred "every day," supported largely by industry news and upbeat company statements. The court held that any theory "will have to show some mechanism for how the truth was revealed," and faulted the alternative corrective-disclosure scenario because it "makes no account for the fact that these disclosures contained non-fraud related information that would have also affected WCG's value." Summary judgment for the defendants was affirmed because the plaintiffs had "failed to present evidence suggesting that the declines in price were the result of the revelation of the truth and not some other factor."

Building the inflation ribbon

In In re Petrobras Securities Litigation, the Southern District of New York described the standard three-step model: "(1) an event study could determine the amount of price inflation in a given security, as well as how much of this dissipated upon disclosures; (2) an 'inflation ribbon' could be constructed, measuring the difference between the inflated price of the security and what it would have traded at without the alleged misrepresentations; and (3) per shares damages could be calculated as the difference between the inflation on the date shares were purchased and the inflation on the date those same shares were sold."

The Fifth Circuit's decision in Ludlow v. BP, P.L.C. (captioned on CourtListener as In re BP, P.L.C. Securities) described its shape: inflation "starts with some positive number" and then, "proceeding in a step-function," "declines by a certain dollar amount after each corrective event is disclosed, eventually ending with zero."

The ribbon must also match the content of each misstatement. In Glickenhaus, the model measured the full disclosure of three concealed practices, but the first actionable false statement addressed only one of them. The court explained that "it can't be the case that the stock price would have fallen fully had this statement reflected the truth," a problem it found minor on that record and "easily resolved on remand." Where statements conceal different facts at different times, the ribbon should reflect that.

Constant-dollar versus constant-percentage inflation

Under the constant-dollar method, as the Fifth Circuit described it in BP, the expert equates the abnormal drop on a corrective disclosure day "with the 'inflation' caused by a preceding misrepresentation," and that amount "is then carried back to the date of the proceeding misrepresentation, such that any share purchased in the interim is deemed 'inflated' by that amount." A $5 abnormal drop means $5 of inflation on every earlier day back to the misstatement, whether the stock then traded at $40 or $80.

The constant-percentage method carries back a proportion instead. The Southern District of New York's opinion in In re Vivendi Universal, S.A. Securities Litigation sets out the formulation at issue there: the best estimate of inflation at purchase is "the percentage change in share price at the point of initial inflation or at the time of revelation of the fraud, as adjusted by market, industry and non-fraud-related company-specific returns during the period between the date of purchase and the date the fraud is revealed (constant percentage inflation)." On that approach, a 10 percent abnormal drop implies $8 of inflation when the stock traded at $80 and $4 when it traded at $40.

Neither method is correct in the abstract. A constant-dollar ribbon fits a misstatement about a fixed sum, such as a concealed liability of known size. A constant-percentage ribbon fits a misstatement that affects value proportionally, such as overstated earnings growth applied to a market multiple. The choice matters most when the price moved a long way during the class period, and each side's expert should tie it to the nature of the concealed fact. In Vivendi, the defendants called the constant-percentage method invalid, but the court held that "damage issues are not properly before it" on a loss causation motion.

Damages models at class certification

Erica P. John Fund, Inc. v. Halliburton Co. (Halliburton I) asked whether plaintiffs "must also prove loss causation in order to obtain class certification" and answered: "We hold that they need not." But Comcast Corp. v. Behrend requires that "a model purporting to serve as evidence of damages in this class action must measure only those damages attributable to that theory."

BP shows how the two fit. For the post-spill class, the defense argued that some corrective events reflected the spill itself rather than the flow-rate misstatements. The Fifth Circuit held that the "fit" between corrective events and misstatements is a common question that need not be resolved at certification, because "Comcast requires a 'sound' methodology, not certainty." Plaintiffs "must prove that the portion of the price fall that they seek in damages is directly attributable to the misrepresentation," but "they do not need to prove it at the certification stage." The model survived because events could be removed: "The ability to do so, not the actual execution of that correction, is what Comcast requires at this stage." For the pre-spill class, which proceeded on a materialization-of-the-risk theory, the court affirmed denial of certification because that damages theory "was not capable of class-wide determination."

How defense experts attack the damages model

  • Mechanism. Show that the alleged disclosures revealed nothing new about the concealed fact, as in Williams.
  • Confounding news. Identify and quantify significant firm-specific news on each event date, the showing Glickenhaus places on the defense.
  • Fit. Argue that price drops reflect the underlying events rather than revelation of the misstatement. At certification this forces a removable-event model; at trial it shrinks the ribbon.
  • Ribbon shape. Challenge full inflation from a first statement that concealed only part of the truth.
  • Carry-back method. Contest constant-dollar or constant-percentage inflation where the price path makes the difference material.
  • Categorical arguments. Avoid overreach. In Petrobras, the court rejected a defense claim that numeric disclosures could have no price effect, finding it "difficult for the Court to accept that, in a reasonably efficient market, a company's stock price would not decline upon reports that it faces billions of dollars in losses."

What to prepare

  • A schedule pairing each misstatement with the corrective disclosures said to reveal it, and the specific concealed fact each one addresses.
  • Event-study results for every corrective date, with all same-day and nearby company news identified and assessed.
  • A written explanation, in nonconclusory terms, of why other firm-specific news did or did not contribute to each decline.
  • The inflation ribbon in both constant-dollar and constant-percentage form, with a reasoned choice between them.
  • A version of the model that can remove any individual corrective event and recompute damages.
  • For any leakage theory, the documents showing how the truth reached the market on each day of leakage.

Supreme Mind builds Expert Witness Simulation. A lawyer points it at a matter and picks a class of expert, such as a defense loss-causation and damages economist, and one run returns a brief in four sections: the expert's likely opinion, ranked cross-examination weaknesses, the Daubert and Rule 702 attack surface, and a directional settlement range. Experts are de-identified composites of a class, never a named individual, supporting quotations are checked verbatim against the public record, and nothing it produces is filed or testifies. A complete sample brief on In re Luckin Coffee is at /sample-brief, and the method is described at /method.

This guide is general information, not legal advice.

Sources

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

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Experts in this guide's practice

Defense event-study econometricianPlaintiff event-study and loss-causation econometricianMarket-efficiency expertSecurities accounting and GAAP expertSection 11 negative causation 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 Exclude05Securities · October 6, 2026Market Efficiency at Class Certification: Cammer and Krogman06Securities · October 13, 2026Loss Causation, Damages and the Inflation Ribbon

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