This is from the non-Butler Snow side of the Blog.

Readers of the Blog know that we believe in strictly applying the requirements of Federal Rules of Evidence 702 and 703.  Long before the 2023 amendments to Rule 702 were a twinkle in the advisory committee’s collective eye, we were pounding the proverbial drum that federal courts should consider the burden on the proponent of the expert opinion testimony and get over the old saw that the Federal Rules favor admissibility.  Drums and saws aside, the Supreme Court’s decision in Daubert and the subsequent amendments to Rule 702 should have obviated the need for our blogospheric advocacy.  The proponent of evidence always bears the burden of establishing its admissibility, and there is no default that a jury should be confronted with junk science and unreliable drivel just because a party—usually the plaintiff, in our experience—paid an expert witness to offer it.  Predictably, we followed closely the steps of what became the 2023 amendments to Rule 702.  We have also followed closely the impact of those amendments, as well as fighting off arguments from the plaintiff lawyers in our own cases that nothing had changed.

So, we were surprised to see a recent decision from an experienced judge that seemed to be mired in exactly the sort of mindset that the 2023 amendments tried to correct.  The case is Thacker v. Ethicon, Inc., No. 5:20cv-50-KKC, 2025 WL 2028082 (E.D. Ky. July 21, 2025), a pelvic mesh remand case, and the defendants made a few challenges to the admissibility of the opinions of plaintiff’s expert, who defendants conceded was a qualified biomedical engineer.  The result is not as noteworthy to us as how the court got there.  For instance, the word “burden” is not found in the opinion.  Nor are any form of the words “demonstrate” or “establish.”  The 2023 amendments are not mentioned.  The cases and secondary authorities cited all pre-date their effective date.  The current Rule 702 is quoted in part, but the omitted portion is mischaracterized in a meaningful way.  The Thacker court started its analysis with:

Under Federal Rules of Evidence 702, an expert witness may testify if

(a) the expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue; (b) the testimony is based on sufficient facts or data; (c) the testimony is the product of reliable principles and methods; (d) the expert has reliably applied the principles and methods to the facts of the case.

Id. at *1.  With omitted language italicized and sometimes bolded, here is the actual language of Rule 702:

A witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwise if the proponent demonstrates to the court that it is more likely than not that:

(a) the expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue;

(b) the testimony is based on sufficient facts or data;

(c) the testimony is the product of reliable principles and methods; and

(d) the expert’s opinion reflects a reliable application of the principles and methods to the facts of the case.

We can give the court a pass for shortening “a witness who is qualified as an expert by knowledge, skill, experience, training or education” to “expert witness” in a case where expertise was not challenged.  We can also let slide saying “testify” without adding “in the form of an opinion or otherwise.”  The rest is problematic.

Consistent with writing the proponent’s “burden” out of the rule, the Thacker court’s analysis of the challenges to the expert’s opinions did not always appear to apply the right standards.  (We will omit discussion of the exclusion of medical opinions and allowance of opinions on the device’s Instructions of Use, given that the 2023 amendments did not change the standards for evaluating the scope of qualifications.) 

The first challenge was to the plaintiff’s expert’s criticism of the defendants’ design control and risk management systems without performing an audit of defendants’ systems.  In rejecting this challenge, the court did use the right standards of the opinion being based on “sufficient facts” and “reliable principles and methods.”  Id.  However, the 2008 case it cited in this section offers an outdated, lower standard:  “[W]here the opinion has a factual basis, it should not be excluded [because] it is up to opposing counsel to inquire into the expert’s factual basis.”  Id. (citation omitted).  The proponent has to establish a “sufficient” factual basis for the expert’s opinions as one of four requirements, not including the expert’s qualifications.  This difference was highlighted in the notes for the 2023 amendment:

First, the rule has been amended to clarify and emphasize that expert testimony may not be admitted unless the proponent demonstrates to the court that it is more likely than not that the proffered testimony meets the admissibility requirements set forth in the rule. See Rule 104(a). This is the preponderance of the evidence standard that applies to most of the admissibility requirements set forth in the evidence rules. See Bourjaily v. United States, 483 U.S. 171, 175 (1987) (“The preponderance standard ensures that before admitting evidence, the court will have found it more likely than not that the technical issues and policy concerns addressed by the Federal Rules of Evidence have been afforded due consideration.”); Huddleston v. United States, 485 U.S. 681, 687 n.5 (1988) (“preliminary factual findings under Rule 104(a) are subject to the preponderance-of-the evidence standard”). But many courts have 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. These rulings are an incorrect application of Rules 702 and 104(a).

The Thacker court’s rejection of the second challenge—that the expert measured the defendants’ systems against standards in ISOs from the International Organization of Standards instead of regulations from the United States FDA—had similar issues.  The court did not measure whether plaintiff carried her burden to establish reliability, but whether defendants proved the opposite, noting “the Defendants [sic] failure to offer any evidence or authority stating that ISOs are irrelevant to medical device manufacturers in the United States.”  Id. at *2.  Notwithstanding Joiner’s ruling that “nothing in either Daubert or the Federal Rules of Evidence requires a district court to admit opinion evidence that is connected to existing data only by the ipse dixit of the expert,” Thacker credited the expert’s ipse dixit that her opinions connected:  “[The expert] plainly opines that ISOs were ‘[t]he primary standards applicable’ to Ethicon’s quality and risk management systems.”  The court also noted that the defendants could cross the expert on the basis for her opinions.  Again, the 2023 notes addressed this dynamic:

Rule 702(d) has also been amended 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 because just as jurors may be unable, due to lack of specialized knowledge, to evaluate meaningfully the reliability of scientific and other methods underlying expert opinion, jurors may also lack the specialized knowledge to determine whether the conclusions of an expert go beyond what the expert’s basis and methodology may reliably support.

Thacker did place two useful qualifiers on admitting the expert’s opinions based on ISOs instead of FDA regulations.  First, notwithstanding Cisson and its questionable progeny, defendants would be permitted to cross the expert “on the subject of FDA regulation compliance.”  Id.  Presumably, defendants would also get to offer other responsive evidence on FDA compliance once plaintiff opens the door.  Second, the expert’s “testimony shall not equate compliance or non-compliance [to her own view of the ISOs] with satisfaction or dereliction of the duty of care.”  Id. at *3.  We could question how the testimony would “help the trier of fact to understand the evidence or to determine a fact in issue,” and can see significant Rule 403 confusion concerns looming.  That reminds us—and perhaps only us—of an older advisory committee note for Rule 704:

The abolition of the ultimate issue rule does not lower the bars so as to admit all opinions. Under Rules 701 and 702 , opinions must be helpful to the trier of fact, and Rule 403 provides for exclusion of evidence which wastes time. These provisions afford ample assurances against the admission of opinions which would merely tell the jury what result to reach, somewhat in the manner of the oath-helpers of an earlier day. They also stand ready to exclude opinions phrased in terms of inadequately explored legal criteria.

Thacker also rejected a challenge that the expert’s opinions were unreliable because she failed to consider a number of risk analyses the defendants performed.  The 2023 notes address this too:

Some challenges to expert testimony will raise matters of weight rather than admissibility even under the Rule 104(a) standard. For example, if the court finds it more likely than not that an expert has a sufficient basis to support an opinion, the fact that the expert has not read every single study that exists will raise a question of weight and not admissibility. But this does not mean, as certain courts have held, that arguments about the sufficiency of an expert’s basis always go to weight and not admissibility. Rather it means that once the court has found it more likely than not that the admissibility requirement has been met, any attack by the opponent will go only to the weight of the evidence.

Thacker found attacks on the breadth of the expert’s review to go to weight and it had already found her methodology had a sufficient basis.  However, the proponent is typically—and, we think, properly—required to justify why cherry-picking what data to consider is consistent with a reliable methodology.  From our perspective, this is part of why it is important to start off with the correct understanding of what it means for the burden to be on the proponent of the expert opinion testimony.