EvidenceProf Blog

Editor: Colin Miller
Univ. of South Carolina School of Law

Tuesday, September 14, 2021

The Proposed Amendment to Federal Rule of Evidence 702

In August, three proposed amendments to the Federal Rules of Evidence were released for public comment. The public comment period closes on February 16, 2022. This is the third in a series of three posts about these amendments. The second proposed amendment is a proposed amendment to Federal Rule of Evidence 702, which currently states that

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:

(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 the principles and methods to the facts of the case.

Under the proposed amendment, Rule 702 would read as follows:

Screen Shot 2021-09-14 at 2.00.32 PM

Under the proposed amendment, there would be two changes to Rule 702.

First, the Rule would clarify that the proponent of an expert witness must satisfy Rule 104(a) rather than Rule 104(b) for the reliability-based requirements of Rule 702. According to the Committee Note, "[t]he amendment clarifies that the preponderance standard applies to the three reliability-based requirements added in 2000—requirements that many courts have incorrectly determined to be governed by the more permissive Rule 104(b) standard."

So, what's the difference? Rule 104(a) requires the proponent to convince the judge of something by a preponderance of the evidence (i.e., more likely than not). Rule 104(b) merely requires the proponent to convince the judge that a reasonable juror could find something by a preponderance of the evidence.

Let's use an example: The prosecution wants to call Erica as an expert witness to testify that she analyzed a latent earprint lifted from the wall of a burglarized home and concluded that there is a good chance it came from the defendant's ear. Under Rule 104(b), the judge could find Rule 704(c) satisfied even if the judge didn't quite think that Erica used reliable principles and methods as long as the judge concluded that a reasonable juror could have found that Erica used reliable principles and methods. The amendment makes clear that a federal judge should only admit expert testimony if she herself believes the expert used reliable principles and methods.


Rule 702(d) has also been amended to emphasize that a trial judge must exercise gatekeeping authority with respect to the opinion ultimately expressed by a testifying expert. A testifying expert’s opinion must stay within the bounds of what can be concluded by a reliable application of the expert’s basis and methodology. Judicial gatekeeping is essential because just as jurors may be unable to evaluate meaningfully the reliability of scientific and other methods underlying expert opinion, jurors may also be unable to assess the conclusions of an expert that go beyond what the expert’s basis and methodology may reliably support. 

The amendment is especially pertinent to the testimony of forensic experts in both criminal and civil cases. Forensic experts should avoid assertions of absolute or one hundred percent certainty—or to a reasonable degree of scientific certainty—if the methodology is subjective and thus potentially subject to error. In deciding whether to admit forensic expert testimony, the judge should (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. Expert opinion testimony regarding the weight of feature comparison evidence (i.e., evidence that a set of features corresponds between two examined items) must be limited to those inferences that can reasonably be drawn from a reliable application of the principles and methods. This amendment does not, however, bar testimony that comports with substantive law requiring opinions to a particular degree of certainty.

This seems huge and possibly the biggest change ever to the Federal Rules of Evidence. It also seems to be a direct response to reports like the report by the President’s Council of Advisors on Science and Technology on the flaws with forensic “feature-comparison” methods, including the analysis of DNA, hair, latent fingerprints, firearms and spent ammunition, toolmarks and bitemarks, shoeprints and tire tracks, and handwriting.

So, what could this change mean? For year, in cases like the Darrell Ewing case we recently covered on Undisclosed, experts would confidently testify that two sets of bullets were fired from the same gun. Conversely, as I noted in a recent blog post, in the prosecution of Tuala Auimatagi, the judge ruled as follows with regard to such testimony:

The judge will permit him to “describe the class characteristics he observed on the bullets” and “[t]he theory of toolmark analysis and how firearms leave markings on bullets or shell casing.”

He will also be allowed “to testify that he cannot exclude or eliminate the bullets as coming from different guns.”

However, “[H]e will not be permitted to describe any greater level of scientific certainty than the bullets may or may not have come from the same gun.”

Under amended Rule 702(d), we might hope/expect to see many similar rulings.



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