Not that long ago (last time we posted), the Sixth Circuit issued an unpublished opinion that affirmed the exclusion of an expert (yay!) but missed the boat on the amendments to Federal Rule of Evidence 702 and its reinforcement of the expert exclusion test (boo!). 

Today, we get to tell you about a published opinion from the Ninth Circuit that affirmed the district court’s exclusion of expert testimony and then summary judgment for lack of evidence of causation (yay!) and very much got on board with the Rule 702 amendments Don’t Say Daubert approach (double yay!). 

The opinion is Engilis v. Monsanto Co., No. 23-4201, __ F.4th __, 2025 U.S. App. LEXIS 20377, 2025 WL 2315898 (9th Cir. Aug. 12, 2025), and it comes out of the Roundup MDL.  Engilis underscores the scrutiny courts must give experts under Rule 702, the necessity for expert opinions to be grounded in sufficient facts and reliable methodology, the importance of scientific experts acting like experts instead of paid partisans, and—most significantly—is a thorough endorsement of the rigorous Rule 702 approach we long have advocated. 

Given that the Ninth was one of the circuits that led the drafters to seek the 2023 Rule 702 amendments, this is cause for celebration indeed.

The Background

Engilis involved a plaintiff who alleged that use of Roundup caused chronic lymphocytic leukemia, a form of non-Hodgkin’s lymphoma.  In support of this claim, he relied on a board-certified oncologist for both general causation (can the product cause the condition?) and specific causation (did it cause the condition in this plaintiff?). 

The district court initially granted the defense motion to exclude on the papers, then granted reconsideration of the specific causation issue and held a Don’t Say Daubert hearing at which the expert was cross-examined.

Specific causation was the question, and the expert had conducted a differential etiology in reaching his opinion that the plaintiff’s cancer was caused by the product, a process which should involve listing all potential causes of the alleged medical condition, then “ruling out” those deemed implausible.

As the author of Engilis (Circuit Judge Morgan Christen) took the time to explain, “differential etiology” is not exactly the same as a “differential diagnosis”: 

In the clinical context, “differential diagnosis” refers to a process for “identifying a set of diseases or illnesses responsible for the patient’s symptoms,” whereas “‘differential etiology’ refers to identifying the causal factors involved in an individual’s disease or illness.”  Put another way, “differential diagnosis actually refers to a method of diagnosing an ailment, not determining its cause,” and “differential etiology . . . is a causation-determining methodology.”  

One potential cause that should have been on the expert’s list was obesity.  The expert had promptly crossed this potential cause off his list based on the “Plaintiff’s Fact Sheet”—the provenance of which was “not clear from the record”.  The fact sheet said plaintiff was “negative” for obesity.  On cross-examination, however, it became clear the expert had no knowledge of whether the plaintiff had obesity; he had never checked the plaintiff’s medical records, and he had not examined him to determine his physical condition either. 

That was an issue—a potential cause was ruled out without sufficient basis for doing so—but the expert’s fallback was that obesity should not have been on the list in the first place.  Contrary to medical literature, the expert said he believed obesity was not a risk factor for non-Hodgkin’s lymphoma, based solely on his “clinical experience”. 

Not good enough. The district court excluded his specific causation opinion, then entered summary judgment for lack of evidence to support the essential element of causation. 

The Ninth Circuit’s Masterpiece

We already gave away the ending of Engilis:  The Ninth Circuit affirms.  In doing so, the court noted that this ultimate result—exclusion of the expert and affirmance of summary judgment—would have been the same under the pre-2023 version of Rule 702 as well as the current version. 

But what makes Engilis such a special case is the work the Ninth Circuit put in to explain the history of Rule 702 and the rigor it requires.  It really is a contrast to the recent Hill decision from the Sixth Circuit, which likewise agreed its expert exclusion affirmance would be the same under either version of Rule 702 but then blindly recited the type of authorities the 2023 Rule 702 amendments sought to move away from.

First, the Ninth Circuit started with a little Rule 702 history lesson.  It recounted the original adoption of Rule 702 in 1975; the Supreme Court’s interpretations of it in Daubert v. Merrell Dow Pharmaceuticals, 509 U.S. 579 (1993) as well as the refinements in General Electric Co. v. Joiner, 522 U.S. 136 (1997), and Kumho Tire Co. v. Carmichael, 526 U.S. 137 (1999); and the codification of the Supreme Court’s Daubert trilogy through the 2000 amendments to Rule 702 which “clearly envisioned a more rigorous and structured approach” to Rule 702 than “some courts were employing” but was not entirely successful in getting all courts to fully embrace that “more rigorous and structured approach”. 

Then, they got to the really good stuff:  the 2023 Amendments to Rule 702, which sought to bolster the rigor of Rule 702 analyses in two main ways: (1) by expressly requiring a proponent of expert testimony to “demonstrate[] to the court that it is more likely than not that” the four admissibility requirements are satisfied; and (2) by also requiring that “the expert’s opinion reflects a reliable application of the principles and methods to the facts of the case.”

Quoting the 2023 Rule 702 Advisory Committee:

This [2023] amendment sought to “clarify and emphasize” that proffered expert testimony must meet the admissibility requirements of Rule 702 by a preponderance of the evidence. … Before the amendment, “many courts” had erroneously held “that the critical questions of the sufficiency of an expert’s basis, and the application of the expert’s methodology, are questions of weight and not admissibility.” Properly applied, Rule 702 requires that challenges to an expert’s opinion go to the weight of the  evidence only if a court first finds it more likely than not that an expert has a sufficient basis to support an opinion. The amendment also aimed “to emphasize that each expert opinion must stay within the bounds of what can be concluded from a reliable application of the expert’s basis and methodology.” “Judicial gatekeeping is essential” to ensure that an expert’s conclusions do not “go beyond what the expert’s basis and methodology may reliably support.”

 Some of the key principles recognized by the Ninth Circuit in Engilis include:

• Burden of Proof Under Rule 702 Does Not Favor Admission: The court reiterated that the proponent of expert testimony always must establish admissibility by a preponderance of the evidence.  Say it with us, and the court:  “[T]here is no presumption in favor of admission.”  Thus, anytime plaintiffs cite earlier Ninth Circuit authorities at us, like Messick v. Novartis Pharms. Corp., 747 F.3d 1193, 1197 (9th Cir. 2014), and Wendell v. GlaxoSmithKline LLC, 858 F.3d 1227, 1232 (9th Cir. 2017), we will cite Engilis back at them, with its rejection of the notion that Rule 702 should be applied with a “’liberal thrust’” favoring admission.
• Reliability and Sufficient Facts Requires Grappling With the Evidence: The Engilis expert goofed in his reliance on his clinical experience to write off published literature.  “Sure there are studies, but I don’t believe them” is not a reasoned, scientifically sound explanation. Clinical experience may be more necessary when a rare disease is at issue, but if studies have dealt with the issue, the expert has to account for them in a reasoned way.  Rule 702 authorities do not stand for the “proposition that an expert’s mere talismanic invocation of ‘clinical experience’ suffices to establish that a differential etiology passes muster under Rule 702.”
• Gatekeeping Function: The Ninth Circuit reaffirmed the district court’s “gatekeeping” responsibility under Rule 702 to ensure that expert testimony is both relevant and reliable before it is presented to a jury.  The court rejected the “let it in and let the jury sort it out” and “goes to weight not admissibility” nonsense.  Here too, it disavowed prior authority like Wendell, which had stated that, where experts’ opinions “are not the ‘junk science’ Rule 702 was meant to exclude,” then, “the interests of justice favor leaving difficult issues in the hands of the jury and relying on the safeguards of the adversary system . . . to ‘attack[] shaky but admissible evidence.'”
• Failure to Rule Out All Causes Must Be Based In Scientifically Sound Reasons:  The court did allow that an expert might reach a causation opinion without ruling out absolutely every possible potential cause, but there has to be a solid evidentiary foundation for the opinion they do reach and a scientifically sound rationale for ruling causes in or out.
• Don’t Say Daubert Hearings Are Permissible, But Not Required.  One expert exclusion area where district courts retain a lot of discretion is “the appropriate form” of an inquiry into the expert’s opinions.  The Ninth Circuit seems to believe that hearings in which the expert is cross-examined are “commonly used” (which to us seems like a bit of an overstatement) but “not required.”  Sometimes an expert’s deficiencies are plainly obvious on paper, but we like that the court seems to approve of hauling a challenged expert before the judge to test their theories.  When scientific issues are complex, it certainly can be helpful to the judge exercising the gatekeeping function to be able to assess the issues in real time.
• If It Isn’t In The Expert’s Report, The Expert Is Asking For Trouble.  The expert in Engilis had prepared a report that assumed the plaintiff was not obese, and when cross-examination revealed that assumption to be flawed, he took issue with medical records reflecting the plaintiff’s BMI by arguing BMI was not a reliable measure of obesity.  Regardless of whether that BMI criticism was accurate, that part of his “opinion was inadmissible for a separate reason: it was not disclosed in his expert report”.  We love this part of the opinion, because all too often we have seen courts readily allow plaintiffs to backfill deficient expert opinions once they are called out.  That is not how it is supposed to work.  Engilis notes:  “The federal rules generally ‘forbid[] the use of any information not properly disclosed.’… . Thus, ‘when a party fails to provide information required by Rule 26, such party “is not allowed to use that information or witness to supply evidence on a motion, at a hearing, or at a trial, unless the failure was substantially justified or is harmless.”’”

Engilis is going to be our go-to on the Rule 702 changes for some time, and we have little doubt the case name is going to become a short-hand for good expert exclusion standards amongst the drug-and-device defense bar.  Now we just have to come to agreement on how to pronounce it. Ang-eh-less?  Ing-liss? An-jill-es?

It might be Dow-burt / Dough-bear all over again…