Supreme Court Should Affirm That FRE 702 Requires Judges To Determine Whether An Expert Opinion’s Factual Basis Is Sufficiently Reliable To Warrant Admissibility
The certiorari petition in this case presents an important question about application of Federal Rule of Evidence 702 (Testimony by Expert Witnesses), as amended in 2023: Is a challenge to the factual basis for an expert’s opinion always a matter of weight for a jury to decide, or must a district judge first determine that the factual basis is sufficiently reliable to warrant admission of the opinion into evidence?
ALF has filed an amicus brief urging the Supreme Court to resolve the inter-circuit split of authority on this frequently recurring question. The brief was authored for ALF by Robert E. Johnston, Aleksandra Rybicki, and Alexa D. Halkias of Hollingsworth LLP.
Whether, under Federal Rule of Evidence 702, challenges to the factual basis of an expert witness’s testimony always go to the weight of the evidence rather than to admissibility, or whether such challenges go to weight only if a court first finds it more likely than not that an expert has a sufficient basis to support the testimony.
Additional Background:
The plaintiff, alleging that she was chronically exposed to ethylene oxide (EtO) emitted into the atmosphere from an industrial facility, filed a putative class action for medical monitoring. A West Virginia district court excluded her expert’s proposed testimony on the ground that its factual underpinnings were insufficiently reliable, and granted summary judgment to the defendant. On appeal, a divided Fourth Circuit reversed, holding that “questions regarding the factual underpinnings of the [expert witness’s] 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).
ALF’s Amicus Brief:
The amicus brief discusses the 2023 amendments to Rule 702, including the reasons that they were adopted. More specifically, the amendments were intended to emphasize a district judge’s expert testimony gatekeeping role to ensure that unreliable opinion testimony is not presented to a jury. This includes a determination by the district judge as to whether the facts and data underlying an expert’s opinion, and the application of the expert’s methodology, are sufficiently reliable to warrant admission of the expert testimony into evidence.
The Supreme Court needs to grant certiorari and hold, contrary to the Fourth Circuit’s opinion, that challenges to the reliability of expert testimony’s factual underpinnings first must be assessed by the trial judge to determine whether they support admissibility of the expert opinion. Such a ruling by the Court would provide clarity and promote uniform application of amended Rule 702.
Contact:
Contact ALF Executive Vice President & General Counsel Lawrence Ebner.
