William & Mary Law Review


Expert testimony is offered at the vast majority of trials in courts of general jurisdiction in the United States. Federal Rules of Evidence 702-06 govern the admissibility of such testimony. In its May 15, 2021, report accompanying the most recent proposed amendment to Rule 702, the Advisory Committee on the Evidence Rules asserts that “many courts” have misapplied Rule 702 by holding that questions as to whether “the expert has relied on sufficient facts or data ... are questions of weight and not admissibility.” Rule 702(b) states that to be admissible, an expert opinion must be “based on sufficient fact or data.” The Committee adds that this error has occurred “in a fair number of cases.”

The Committee’s criticism is valid—but incomplete. The central contention of this Article is that another major, contributing cause to the problem is the courts’ misunderstanding of the relationship between the expression “scientific ... knowledge” in Rule 702 and the expressions “facts” or “facts or data” which appear in Rules 702(b), 702(d), 703, and 705. This Article contends that properly interpreted, the latter expressions include only case-specific information, not research data relevant to the validation of the expert’s methodology as reliable “scientific ... knowledge.”

Positing that interpretation, this Article then attempts to clarify the judge’s and jury’s roles in evaluating the credibility, quality, and quantity of the factual bases for proffered expert opinions. More specifically, the Article argues that the jury has the exclusive authority to pass on the credibility of the testimony about the factual bases of admitted opinions. However, before admitting the opinion, the judge must assess the quality of the type of case-specific information that the expert contemplates relying on. If the information takes the form of secondhand reports about out-of-court statements, under Rule 703 the judge must determine whether the “experts in the particular field would reasonably rely on those kinds of facts or data.”

Moreover, again before allowing the expert to submit his or her opinion to the jury, under Rule 702(b) the judge must independently assess the quantity of the information. For example, if an accident reconstruction expert proposes opining about the point of impact (POI) in a case, the judge must inquire whether the expert has identified enough case-specific information such as testimony about the vehicles’ final resting places and the location of the debris to adequately support a conclusion about POI.

These conclusions not only respect the legitimate authority of both judge and jury, but they also give the Rule provisions on expert testimony logical coherence.

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