Recent Amendments to the Rules Governing Admissibility
of Expert Testimony in Federal Rule of Evidence 702

In litigation, everything ultimately boils down to proof; that is, how the parties prove their claims and defenses. One way that parties do this is through witness testimony.

There are two kinds of testifying witnesses: lay witnesses and expert witnesses. Lay witnesses may only testify about matters on which they have personal knowledge. Expert witnesses, however, may give opinion testimony about scientific, technical, or other specialized issues in the case on which they need not have personal knowledge, if the testimony meets certain criteria under the applicable evidentiary rules.

The Recent Amendments to FRE 702

Federal Rule of Evidence 702 (“FRE 702”) governs the admissibility of expert witness testimony in federal court cases. Generally, expert testimony is only admissible under FRE 702 if: (1) the expert is qualified to provide opinion testimony on the issue at hand; (2) the expert’s testimony will help the factfinder understand the evidence or determine a fact at issue; and (3) the expert used a reliable methodology to support his or her opinions.

Parties frequently file pre-trial motions to exclude expert witness testimony on the grounds that the testimony does not satisfy FRE 702’s reliability requirements. The district court typically decides these motions before trial. Because many cases hinge on expert testimony, a district court’s decision to admit or deny such testimony can drastically sway the jury’s verdict. For that reason, a district court serves as the “gatekeeper” for expert testimony, meaning, the district court should allow only reliable expert testimony to pass through the “gate” and into evidence. The issue, however, is that unreliable expert testimony oftentimes passes through the gate and on to the jury.  

For example, in United States v. Watkins, a fingerprint expert was allowed to testify that “the error rate for identification is zero” (emphasis added). This testimony led the jury to believe that the expert’s methodology was infallible, which, in turn, caused the jury to view the expert’s testimony as more reliable than it truly was.

Watkins is not an outlier; many other federal courts have adopted similar applications of FRE 702. In several of these cases, district courts have incorrectly held that the reliability-based requirements in FRE 702 are issues of weight for the jury to determine rather than issues of admissibility for the court to decide.

For these reasons, FRE 702 was recently amended to clarify the district court’s gatekeeping responsibility. The amendment, which went into effect on December 1, 2023, provides:

“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:

1. 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;
2. the testimony is based on sufficient facts or data;
3. the testimony is the product of reliable principles and methods; and
4. the expert’s opinion reflects a reliable application of the principles and methods to the facts of the case.”

Clarifying the Evidentiary Burden under FRE 702

The amendment to the first paragraph FRE 702 does not substantively change the rule. Rather, this amendment simply clarifies that the preponderance standard applies to FRE 702, which has been the standard since the United States Supreme Court decided Daubert v. Merrell Dow Pharmaceuticals, Inc. in 1993.

However, this amendment was necessary because many district courts had abandoned Daubert for a more relaxed evidentiary standard — in some cases, even finding a presumption that expert testimony is admissible. Thus, the Advisory Committee on Evidence Rules inserted the preponderance standard directly into the text of FRE 702, eliminating any doubt that it is the proponent of the expert testimony who bears the burden of proving that the testimony is admissible; not the opponent’s burden to disprove.

Although the amendment does not change the substance of FRE 702, the amendment will likely change how practitioners approach expert testimony. In particular, the amendment invites opponents to exclude expert testimony because the preponderance standard now appears on the face of FRE 702. Therefore, the proponent of expert testimony should take greater care to ensure that he or she can prove, by a preponderance of the evidence, that the expert’s testimony satisfies all of the requirements of FRE 702(a) – (d).

Preventing Overstatements by Expert Witnesses

The amendment to FRE 702(d) clarifies that expert testimony should be excluded where the expert’s methodology or opinions are unreliable. Indeed, by changing the text FRE 702(d) from “the expert has reliably applied” to “the expert’s opinion reflects a reliable application,” this amendment underscores that the district court’s gatekeeping responsibility extends to an expert’s methodology and opinions.

The Advisory Committee explained that this amendment was necessary because it is difficult for most jurors to determine whether an expert’s opinions are supported by the expert’s methodology. Therefore, by clarifying that the district court’s gatekeeping responsibility extends to FRE 702(d), the amendment confirms that the court should decide whether an expert witness’s conclusions go beyond what the expert’s basis and methodology may reliably support.

In practice, the amendment to FRE 702(d), coupled with the explicit addition of the “preponderance” standard in the first paragraph of FRE 702, will likely result in an increase in pre-trial motions to exclude expert witness testimony. Indeed, under the amended FRE 702, district courts are to ensure that the proponent of the expert witness’s testimony proves all of the criteria for admissibility by a preponderance of the evidence. That could very well mean that more expert testimony will be excluded from evidence at trial.

Therefore, parties should be extra diligent when vetting expert witnesses to retain in federal court cases, and should make sure that whomever they retain understands the criteria for admissibility in the amended FRE 702 and testifies within those bounds. The expert’s failure to do so could have dire consequences for the proponent of the testimony.