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.
The more interesting aspect of Engilis is its threshold discussion of the parties’ dispute over “the significance of the 2023 amendment to Rule 702 and the effect of that amendment on our existing precedent.” The district court issued its ruling two weeks before the 2023 amendments took effect, so both the district court and the Ninth Circuit applied the pre-amendment version of the Rule. But the Ninth Circuit reasoned that it was a distinction without a difference, because the “decision would be the same under either version of the Rule.” As part of its impressively detailed exposition of the history of Rule 702 and the Ninth Circuit’s case law interpreting and applying it, the panel concluded:
[I]nsofar as the parties argue about the degree to which the amendments establish, or refute, that Rule 702 is a “liberal” standard that favors admission as “the rule, not the exception,” we confirm that a proponent of expert testimony must always establish the admissibility criteria of Rule 702 by a preponderance of the evidence and that there is no presumption in favor of admission.
Engilis, 2025 WL 2315898 at *6 (emphasis added). Instead, Ninth Circuit precedent has “long recognized” that a proponent of expert evidence must establish by preponderance of proof that the admissibility criteria in Rule 702 have been satisfied. While acknowledging that earlier precedent held that “Rule 702 should be applied with a ‘liberal thrust’ favoring admission,” the Engilis court explained that “Rule 702 liberalized the admission of expert testimony as compared to the Frye test, but it did not establish a categorical preference for admitting expert testimony.” Thus, Ninth Circuit law “should not be understood to suggest a presumption of admission,” because “[t]here is no such presumption.” Id. Rather, as the panel noted, Ninth Circuit precedent is “[c]onsistent with the 2023 amendment” in requiring the proponent of expert testimony “to demonstrate each of the requirements of Rule 702 by a preponderance of the evidence.”
But the 2023 amendment had another major purpose, and the Engilis panel tracked it as well. As the panel noted, the advisory committee note to the 2023 amendments explained that “many courts” had been incorrectly treating “the critical questions of the sufficiency of an expert’s basis, and the application of the expert’s methodology, [as] questions of weight and not admissibility.” While acknowledging specific Ninth Circuit precedent that had held “shaky” opinions should be allowed to proceed to a jury and that the Rule 702 focus should be on the soundness of an expert’s methodology rather than the correctness of an expert’s opinion, the Engilis panel observed that “‘shaky’ expert testimony, like any expert testimony, must still be ‘admissible,’ and this requires a determination by the trial court that it satisfies the threshold requirements established by Rule 702.”
Ultimately, the Engilis decision reaffirms the importance of the district courts’ gatekeeping function. Although it was decided based on Rule 702 as it existed prior to the 2023 amendment, it embraces two core purposes of the amendment. The main takeaway is that, while the Ninth Circuit did not disavow any of its pre-amendment cases applying Rule 702, it expects those cases to be applied through the lens of the advisory committee’s clarification of the admissibility requirements.
