Expert Witness Archives - Faegre Drinker on Products

Subject: Expert Witness

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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Paraquat MDL Lone Pine Order Creates New Hurdles for Nonsettling Plaintiffs

The multidistrict litigation (MDL) concerning paraquat-based herbicides — In re: Paraquat Products Liability Litigation, MDL No. 3004 (S.D. Ill.) — has become a focal point in mass torts. Thousands of plaintiffs allege that exposure to paraquat caused them to develop Parkinson’s disease (PD). The litigation has featured high-stakes scientific disputes, key defense wins, a master settlement agreement, and now Case Management Order No. 25 (CMO 25, 2026 WL 1707147), a Lone Pine order with important implications for nonsettling plaintiffs and a potential roadmap for effective case management in other MDLs.

In April 2024, the MDL court excluded the plaintiffs’ sole expert on general causation. That ruling left the plaintiffs unable to establish general causation, and the court accordingly granted the defendants’ motion for summary judgment. But that ruling only formally applied to the four bellwether cases; while the bellwether plaintiffs’ inability to establish general causation portended problems for every plaintiff in the MDL, the litigation continued.

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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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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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ChatGPT As Your New Testifying Expert Under Proposed Federal Rule of Evidence 707? Maybe Not.

Artificial intelligence is taking the world by storm, and the legal community is no exception. Tools that can reduce the time and cost of litigation have long been in high demand by both clients and counsel. But the tool must be fit for its purpose, and tools that generate evidence or other outputs that will be submitted to the court must pass judicial scrutiny. As video cameras became smaller and less expensive, there were fights over the admissibility of deposition videos that attorneys had recorded themselves to avoid videographer fees. Practitioners who focus on e-discovery can tell stories of hotly litigated technology-assisted review protocols. One of the newer fights concerns the admissibility of machine-generated “expert” opinions.

The U.S. Courts Advisory Committee on the Federal Rules of Evidence (the “Committee”) proposes to address the issue by adding a new rule, Federal Rule of Evidence 707. The prospect of adding a new rule to regulate the admissibility of machine-generated evidence was first raised at the Committee’s November 2024 meeting. Since then, the Committee has proposed the following language for Rule 707:

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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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