Daubert Archives - Faegre Drinker on Products

Subject: Daubert

Third Circuit Confirms Correlation Still Does Not Prove Causation

A recent Third Circuit decision is a useful and quotable reminder that temporal correlation is not enough to prove causation.

Causation is an indispensable element of any product liability action. It is the same in pharmaceutical third-party payor (TPP) class actions, where it is often the element most likely to defeat class certification. Unsurprisingly, plaintiffs often employ creative workarounds in an effort to sidestep obvious causation problems. In In re Avandia Marketing, Sales Practices and Products Liability Litigation, — F.4th —, 2026 WL 2093904 (3d Cir. July 21, 2026), the Third Circuit made clear that there are no shortcuts.

According to the plaintiff TPPs, the defendant pharmaceutical manufacturer had marketed the medication at issue as not only treating diabetes but offering cardiovascular benefits too. The plaintiffs claimed that the promotional campaign caused physicians to prescribe the medication at inflated rates, forcing the plaintiffs to reimburse prescriptions they would not otherwise have covered.

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Treat Your AI Like an Opposing Expert: Rule 702 Lessons for Evaluating AI Output

Attorneys using generative AI can borrow a familiar litigation skill: Evaluate AI-generated output the way they would evaluate an opposing expert witness opinion under Federal Rule of Evidence 702. An expert witness cannot simply “waltz into the courtroom and render opinions” without adequate foundation. Clark v. Takata Corp., 192 F.3d 750, 759 n.5 (7th Cir. 1999). Nor can an expert bridge the gap between data and conclusion with nothing more than ipse dixit — the expert’s own say-so. Gen. Elec. Co. v. Joiner, 522 U.S. 136, 146 (1997).

Rule 702 imposes that discipline directly. It requires expert testimony to be “based on sufficient facts or data,” be “the product of reliable principles and methods,” and reflect “a reliable application of the principles and methods to the facts of the case.” So, when an opposing expert offers an opinion, a litigator’s instinct is not to accept it but to probe its basis and reliability.

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Close, But Not Quite: Eastern District of North Carolina Excludes Experts Whose General Expertise Does Not Enable Specific Opinions Offered

Even “[a] supremely qualified expert cannot waltz into the courtroom and render opinions” unless those opinions pass muster under Federal Rule of Evidence 702. Clark v. Takata Corp., 192 F.3d 750, 759 n.5 (7th Cir. 1999). As a recent case from the Eastern District of North Carolina illustrates, this principle is at play not only when critiquing an expert’s methodology, but also the expert’s expertise.

In Williams v. Sig Sauer, Inc., — F. Supp. 3d —, 2025 WL 2643400 (E.D.N.C. Sept. 8, 2025), the plaintiff was an “enforcer” for his motorcycle club who “protect[ed]” and “monitor[ed]” the club members. He alleged that his pistol discharged and injured him while he was adjusting his position on his motorcycle. In support of his product liability claims against the manufacturer of the pistol, he proffered two expert witnesses: a gunsmith and a mechanical engineer. The defendant moved to exclude both experts and filed a motion for summary judgment.

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Nothing Shocking Here – Eleventh Circuit Affirms Defense Win in Electroconvulsive Therapy Case

When a case involves electroconvulsive therapy (ECT), one might think it originated out of the Twilight Zone. Despite the misrepresentation of such therapies in popular media, modern ECT serves as a valuable option for patients with certain severe mental health conditions who have tried other therapies without success. Although ECT is far safer today than it was when the stigma attached to it was formed, it still carries risks such as confusion, memory loss, and some physical side effects. One need not enter another dimension to envision why a plaintiff might claim damages arising from those risks. Much like Rod Serling’s anthology, the Eleventh Circuit recently closed the door on one such episode.

In Thelen v. Somatics, LLC, — F.4th —, 2025 WL 2749888 (11th Cir.), the plaintiff suffered from depression and mental health issues so severe that he attempted to take his life numerous times in numerous ways. During a two-year span, he received 95 ECT treatments to address his conditions. He was later diagnosed with a neurocognitive disorder that caused severe memory loss.

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Clearing the Weeds: The Ninth Circuit Confirms that There is Not (And Never Has Been) a Presumption of Admissibility in Its Case Law Addressing Rule 702

The judge overseeing the In re Roundup Products Liability Litigation MDL once remarked that “When you [consider] Ninth Circuit law, you come away with a pretty strong feeling that the Ninth Circuit is more tolerant of shaky expert opinions than other circuits.” But that was before the 2023 amendments to Federal Rule of Evidence 702, and appellate courts around the country have gradually been addressing how the amendments impact pre-amendment case law. The Ninth Circuit recently joined the ranks in a way, affirming that same judge’s exclusion of an expert’s causation opinion while harmonizing Ninth Circuit case law with the purposes of the 2023 amendments. The opinion is Engilis v. Monsanto Company, — F.4th —, 2025 WL 2315898 (9th Cir. 2025), and the headlines may come as a surprise to some.

The case-specific underpinnings of the holding are relatively straightforward. The plaintiff alleged that he developed cancer due to exposure to a product manufactured by the defendant. His expert, however, had failed to consider the plaintiff’s obesity as a potential cause of the cancer when conducting the differential etiology that formed his specific causation opinion. He tried to get around this omission by claiming that the plaintiff was not obese, and the plaintiff argued that this was a disputed fact because his plaintiff’s fact sheet was marked “negative” for obesity. However, the expert failed to cite any medical records indicating that the plaintiff was not obese and did not engage with records that showed he was obese. Translated to Rule 702 terms, any opinion that the plaintiff was not obese was not “based on sufficient facts or data.” So, the expert argued that obesity is not a risk factor for the kind of cancer at issue and thus did not need to be considered. But his report cited no support for that proposition, which he manufactured at the hearing on the defendant’s Rule 702 motion. The Ninth Circuit agreed with the district court that these issues rendered the expert’s specific causation opinion inadmissible.

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Defining the Limits of Lay Testimony in Complicated Products Cases

“So when is a question too complicated for the jury?” That is the question the Third Circuit sought to answer recently in Slatowski v. Sig Sauer, Inc., ___ F. 4th ___, 2025 WL 2178533 (3d Cir. 2025), reversing a district court’s grant of summary judgment despite affirming its exclusion of the plaintiff’s causation experts. Ironically, the Third Circuit’s analysis of when an expert opinion is required is itself so nuanced that it may require expert interpretation. Upon close inspection, the Slatowski panel’s holding is not nearly as broad as the headings might suggest.

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