Insights & Events

Hollingsworth LLP and the Atlantic Legal Foundation (ALF) filed an amicus curiae brief in support of the petition for certiorari filed by Union Carbide Corporation and Covestro LLC in Union Carbide Corp. v. Sommerville (25-919). The brief urges the Supreme Court to accept the case in order to correct the Fourth Circuit’s misapplication of Federal Rule of Evidence 702 as clarified by the 2023 amendments and Advisory Committee Notes.

The respondent, Lee Ann Sommerville, filed a putative class action for medical monitoring in the Southern District of West Virginia alleging that residential exposure to ethylene oxide emissions from petitioners’ facilities increased her risk of developing cancer in the future. Respondent’s expert witness used an air model to calculate respondent’s potential cumulative exposure to ethylene oxide from the facilities during the relevant time period. In its role as gatekeeper, the district court properly excluded the air modeling expert, finding that the expert’s application of the underlying data “was methodologically flawed, full of unsubstantiated assumptions, and not scientifically sound,” and granted summary judgment.

The Fourth Circuit reversed, holding that “questions regarding the factual underpinnings of the [expert witness’] opinion affect the weight and credibility of the witness’ assessment, not its admissibility.” Sommerville v. Union Carbide Corp., 149 F.4th 408, 423 (4th Cir. 2025). The Fourth Circuit solely relied on cases decided before the 2023 amendments to Rule 702, specifically Bresler v. Wilmington Trust, 855 F.3d 178 (4th Cir. 2017), which directly conflicts with amended Rule 702.

Hollingsworth LLP’s amicus brief juxtaposes the Fourth Circuit’s erroneous application of the expert admissibility standard with the origin, purpose, and intended impact of amended Rule 702. The brief explains that in promulgating the 2023 amendments, the advisory committee members criticized cases like Bresler for misstating the admissibility standard and the Chair of the Subcommittee that drafted the 2023 amendments specifically called out Bresler for being inconsistent with the standards set forth in the rule.

The brief discusses the 2023 amendments that were designed to reinforce a trial judge’s gatekeeping duty and prevent unreliable expert testimony from being presented to a jury. As clarified by the 2023 amendments, Rule 702 requires the district judge to determine whether the facts and data underlying an expert’s opinion, the application of the expert’s methodology, and the methodology itself, are sufficiently reliable to warrant admission of the expert testimony into evidence. The history and plain language of Rule 702 clarify that questions on the factual basis of an expert’s opinions are questions of admissibility for the judge, not questions of weight for the jury.

The amicus brief requests that the Supreme Court grant certiorari to address the impact of the 2023 amendments to Rule 702 and provide clear guidance regarding the proper interpretation of Rule 702 to harmonize the standard on the admissibility of expert testimony across all circuits. The amicus brief cautions that without a ruling from the Supreme Court, “litigants will continue to face uncertainty in how Rule 702 should be applied, admissibility standards that vary by circuit, and the same wayward decisions that necessitated the rule’s amendment.”