Rule 702 Amendments Will Likely Lower Courts’ Tolerance of “Shaky” Expert Witness Testimony

Category: Articles Tags: Expert WitnessRule 702 Amendments

The long-awaited amendments to Federal Rule of Evidence 702 took effect across federal courts on December 1, 2023.  Companies and individuals whose trial and settlement outcomes come down to expert witness testimony should pay close attention to the growing body of caselaw defining the import of these amendments.

Rule 702 provides a key tool for litigants to keep “junk science” out of trial, and imposes on courts an important “gatekeeping” responsibility to exclude any expert opinions that lack sufficiently reliable methodologies.  Although “[n]othing in the amendment[s] imposes any new, specific procedures” to the rule, the Advisory Committee’s comments strengthen the rule in a number of ways.

The amendments therefore require litigants to take special care in selecting their expert witnesses and preparing them for trial.  They also create more promising opportunities for litigants to challenge baseless or weak expert opinions offered by adversaries.

Rule 702 Amendments “Clarify” and “Emphasize” Courts’ Gatekeeping Responsibilities

With the new amendments, Federal Rule of Evidence 702 now reads as follows (amendments are italicized and underlined):

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 has reliably applied expert’s opinion reflects a reliable application of the principles and methods to the facts of the case.

As noted in its comments, the Advisory Committee intended for its amendments to “clarify” and “emphasize” courts’ gatekeeping responsibilities under the rule.  Consequently, courts have treated the amendments as clarifications or reminders of the standard, rather than changes to it.  The United States Court of Appeals for the Fourth Circuit, for instance, cited the amendments before their effective date in reversing a $4.8 million wrongful death verdict obtained in part through unreliable expert witness testimony.[1]  Other courts have similarly noted that the admissibility analysis often “remain[s] the same” under the new and previous versions of the rule.[2]

Practice Pointers

Nevertheless, the Advisory Committee’s comments strengthen the rule and bring to light a number of focus areas for parties—both in preparing their own experts, and challenging expert opinions offered by the opposing party.

  1. Prepare Your Experts for Increased Scrutiny, and Take Advantage of Opportunities to Challenge Questionable Expert Opinions Offered by Adversaries.

The 2023 amendments make clear that proponents of expert testimony have the burden, “by a preponderance of the evidence,” to establish that the testimony satisfies Rule 702 requirements.  This standard comes from Federal Rule of Evidence 104(a), and squarely places the threshold assessment of an expert’s factual basis and methodologies with the district court.

In recent years, some courts had taken lax approaches to the rule and punted questions surrounding “shaky” expert opinions to the jury.[3]  The 2023 comments explain that Rule 702 does not allow for such approaches: although an expert’s opinion can be admitted notwithstanding relatively insignificant reliability concerns, it is “incorrect” for courts to treat “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.”  Courts must instead address such “critical questions” head on at the admissibility stage, before the expert opinion reaches the jury, and exclude any expert evidence that is not sufficiently reliable.

As a result, litigants seeking to introduce expert witness testimony should prepare their experts for increased scrutiny, including of the expert’s qualifications and methodologies.  Conversely, a litigant seeking to exclude an expert’s testimony should fully embrace this standard and, where appliable, note the proponent’s inability to demonstrate the sufficiency of its expert’s qualifications and methodologies by a preponderance of the evidence.

  1. Ensure Consistency Between the Certainty of Your Own Expert’s Opinions and Known Error Rates of Their Methodologies, and Note Any Mismatches Present in Your Opponent’s Expert Evidence.

The comments expressly warn that “forensic experts” should “avoid assertions of absolute or one hundred percent certainty—or to a reasonable degree of scientific certainty—if the methodology [utilized in forming their opinions] is subjective and thus potentially subject to error.”  The comments also instruct courts to “(where possible) receive an estimate of the known or potential rate of error of the methodology employed, based (where appropriate) on studies that reflect how often the method produces accurate results.”

Although focused on forensic experts, the import of this guidance applies to expert methodologies in a wide range of industries—such as forensic fingerprint matching analyses with certain error rates; medical diagnostic methods known to have certain false positive rates; or certain statistical analyses with known confidence intervals.  Litigants should ensure a match between their own experts’ methodologies and the degree of certainty with which they offer their opinions, and those lodging expert challenges should highlight mismatches between the two.

  1. Take Note of Subjectivity Involved in an Expert’s Opinions.

Relatedly, parties should take note of the comments’ indication that “subject[ivity]” can make expert opinions “potentially subject to error.”  Expert opinions may involve some level of subjectivity in certain types of cases—for instance, medical experts often must choose between two possible, but conflicting diagnoses; auto accident reconstruction experts must sort between competing theories and possible causes of accidents; and financial and accounting experts often form working assumptions in calculating an individual’s lost income or a company’s lost profits.  While some subjectivity can be tolerated under the rule, expert conclusions that involve more subjective than objective factual analysis run the risk of exclusion under the new Rule 702.

  1. Ensure Your Experts Comply with Basic Principles of the Scientific Method, and Challenge Expert Opinions That Do Not.

The amendments require that the expert’s opinion reflect a reliable application of scientific methods and principles to the facts of the case.  These methods and principles often come from industry-specific standard and guidance, such as American Society for Testing and Materials (“ASTM”) standards, and Occupational Safety and Health Administration (“OSHA”) or other workplace health and safety standards.

Importantly, however, Rule 702 also requires compliance with basic principles of the “scientific method”—including assessment of hypotheses through replicable tests and investigation and consideration of all relevant facts (both “good” and “bad”).[4]  The Rule 702 amendments provide more opportunities to challenge experts who fail to do so, whether through “cherry pick[ing]” from relevant data or resorting to “result-driven” reasoning.[5]  Conversely, parties preparing their experts should put their experts to the test and correct any shortcomings in their investigation and analysis prior to offering their opinions.


Although the December 2023 amendments ostensibly “clarify” what Rule 702 has required of experts all along, parties can expect courts, and each other, to treat expert testimony with increased scrutiny.  Litigants should carefully review the amendments and comments as a checklist for ensuring their experts’ opinions are admissible.  And those faced with “shaky” expert opinions from opponents should treat the amendments and comments as a playbook for planning their modes of attack.

Gentry Locke lawyers frequently prepare litigation experts for trial and handle admissibility challenges under Rule 702 and its state law counterparts.  Call us for more information or assistance in navigating the new amendments.

[1] Sardis v. Overhead Door Corp., 10 F.4th 268 (4th Cir. 2021).
[2] E.g., Brown v. Saint-Gobain Performance Plastics Corp., No. 22-cv-018-LM, 2023 U.S. Dist. LEXIS 230628, at *4 n.1 (D.N.H. Dec. 29, 2023).
[3] See, e.g., Hardeman v. Monsanto Co., 997 F.3d 941, 962 (9th Cir. 2021) (citing Daubert v. Merrell Dow Pharms., Inc., 509 U.S. 579, 596 (1993)) (finding no error in trial court’s “slight deference” to experts with “borderline opinions” on the ground that “[t]he interests of justice favor leaving difficult issues in the hands of the jury” and relying on the trial process to “attack shaky but admissible evidence”).
[4] In Re Lipitor (Atorvastatin Calcium) Mktg. v. Pfizer, Inc., 892 F.3d 624, 634, (4th Cir. 2018) (noting that courts “consistently” exclude expert opinions formed through “result-driven analysis, or cherry picking” of data because “such an approach does not reflect scientific knowledge, is not derived by the scientific method, and is not good science”) (internal citations and quotations omitted).
[5] See n. 4.  Although the 2023 Advisory Committee comments do not specifically address the scientific method, the emphasis of courts’ gatekeeping responsibilities will likely result in an increased focus on this topic at the admissibility stage.  The comments note that “[j]udicial gatekeeping is essential because . . . jurors may . . . lack the specialized knowledge to determine whether the conclusions of an expert go beyond what the expert’s basis and methodology may reliably support.”

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