Getting an Expert Opinion Admitted

Who has to prove what, and to whom

Admissibility of expert opinion in federal court is a preliminary question for the judge. FRE 104(a) assigns the court the task of deciding “any preliminary question about whether a witness is qualified, a privilege exists, or evidence is admissible,” and provides that in so deciding “the court is not bound by evidence rules, except those on privilege.” The party offering the opinion — the proponent — carries the burden, and carries it by a preponderance of the evidence.

Since 1 December 2023 that allocation appears on the face of FRE 702 itself. The rule now permits a qualified witness to testify in the form of an opinion “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.”

Four elements, four separate showings. A proponent who establishes qualification and stops has answered one part of a four-part demand. Courts routinely admit some of an expert's opinions and exclude others, which is what happens when the four elements are applied opinion by opinion rather than witness by witness.

Where the reliability language actually came from

The chronology matters, because a great deal of secondary writing collapses it. Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993), was decided under a version of Rule 702 that contained none of the reliability criteria now at (b), (c) and (d). The rule then read, in full: “If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise.” The Court derived the gatekeeping obligation from the words “scientific … knowledge” and “assist the trier of fact.”

The three reliability requirements were added by amendment effective 1 December 2000, in response to Daubert and to Kumho Tire Co. v. Carmichael, 526 U.S. 137 (1999). The amendment effective 1 December 2011 was part of the general restyling of the Federal Rules of Evidence and made no substantive change. The amendment effective 1 December 2023 touched only two things: the preamble, which now states the burden and the quantum of proof, and subsection (d), which was rewritten from “the expert has reliably applied the principles and methods to the facts of the case” to “the expert's opinion reflects a reliable application of the principles and methods to the facts of the case.” Subsections (a), (b) and (c) are word for word what they were in 2000.

Why the 2023 amendment reads as a correction, not a new bar

The Advisory Committee described the amendment as a repair of judicial error rather than a change of standard. Its note explains that the rule was 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,” and states the reason bluntly: “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 strongest evidence that 2023 created nothing new is the Committee's own note to the 2000 amendment, which had already said: “the proponent has the burden of establishing that the pertinent admissibility requirements are met by a preponderance of the evidence.” The 2023 amendment exists because that sentence sat in a Committee note for twenty-three years and a body of case law grew up around the rule's silence.

Three further statements in the 2023 note cut against reading it as uniformly pro-exclusion. “Nothing in the amendment imposes any new, specific procedures.” The amendment does not “require that the court make a finding of reliability in the absence of objection.” And courts that have demanded expert testimony “appreciably help” the trier of fact are applying a standard the Committee called “unnecessarily strict.” The note adds that the Rule 104(a) standard “does not require perfection” and does not require a court “to nitpick an expert's opinion.”

Reliability is a lower bar than correctness

The single most useful proposition available to a proponent is that Rule 702 asks whether the opinion is reliable, not whether it is right. The 2023 note quotes the 2000 note quoting In re Paoli R.R. Yard PCB Litigation, 35 F.3d 717, 744 (3d Cir. 1994): proponents “do not have to demonstrate to the judge by a preponderance of the evidence that the assessments of their experts are correct, they only have to demonstrate by a preponderance of evidence that their opinions are reliable. … The evidentiary requirement of reliability is lower than the merits standard of correctness.”

The Committee applied that directly to the ordinary case of duelling experts: “It will often occur that experts come to different conclusions based on contested sets of facts. Where that is so, the Rule 104(a) standard does not necessarily require exclusion of either side's experts. Rather, by deciding the disputed facts, the jury can decide which side's experts to credit.” Disagreement between two competent experts is not, by itself, a reliability problem for either of them.

The note also preserved a genuine weight category. If the court finds it more likely than not that an expert has a sufficient basis, “the fact that the expert has not read every single study that exists will raise a question of weight and not admissibility.” What the Committee rejected is the inference that sufficiency of basis always goes to weight.

The factors are not a checklist, and often not the right factors

Daubert identified considerations bearing on reliability — whether the theory or technique can be and has been tested, whether it has been subjected to peer review and publication, the known or potential rate of error together with the existence and maintenance of standards controlling the technique's operation, and general acceptance. The sentence that introduces them is the one to keep attached to them: the Court did not “presume to set out a definitive checklist or test.” 509 U.S. at 593. It added that “[t]he inquiry envisioned by Rule 702 is … a flexible one.” Id. at 594. Kumho Tire repeated the point: the listed factors “neither necessarily nor exclusively appl[y] to all experts or in every case.”

Kumho Tire also settled that the gatekeeping obligation applies “not only to testimony based on ‘scientific’ knowledge, but also to testimony based on ‘technical’ and ‘other specialized’ knowledge.” An experience-based witness is inside the framework; what changes is which reliability criteria fit. The test the Court supplied for that witness is whether the expert “employs in the courtroom the same level of intellectual rigor that characterizes the practice of an expert in the relevant field.”

For a non-scientific expert the five additional considerations compiled in the 2000 Advisory Committee note are usually the better fit than the Daubert list: whether the opinion grew out of independent research or was developed expressly for testifying; whether the expert unjustifiably extrapolated from an accepted premise to an unfounded conclusion; whether obvious alternative explanations were adequately accounted for; whether the expert is being as careful as in regular professional work outside paid litigation consulting; and whether the field is known to reach reliable results for the type of opinion offered. These are the Committee's compilation of lower-court practice, not Supreme Court holdings, and should be attributed that way.

The showing is made from a record that is already fixed

By the time admissibility is briefed, the proponent's evidence is largely closed. FRCP 26(a)(2)(B) requires a written report from a retained expert containing the opinions and their bases; FRCP 26(b)(4)(A) makes the expert deposable as of right once identified, and sequences the deposition after the report. The report and the transcript are the exhibits to the opposition brief. Because Rule 104(a) frees the court from the rules of evidence on the admissibility question, both can be considered even though both are hearsay.

The practical consequence is that the reliability showing is built during the engagement, not during the briefing. An opinion whose stated methodology is described in the report, applied visibly to the case-specific facts, and defended coherently in deposition presents the court with a straightforward preponderance question. An opinion whose method is announced rather than shown leaves the proponent arguing from counsel's characterization of what the expert must have done, which is the posture in which motions succeed against it.

What the court must do, and what happens on appeal

The trial court has wide discretion in how it performs the gatekeeping function and none as to whether it performs it at all. The Tenth Circuit's formulation in Dodge v. Cotter Corp., 328 F.3d 1212 (10th Cir. 2003), quoting Goebel v. Denver & Rio Grande Western R.R. Co., 215 F.3d 1083, 1088 (10th Cir. 2000), is that the record “must adequately demonstrate by specific findings on the record that it has performed its duty as gatekeeper,” and that in the absence of such findings a court of appeals “must conclude that the court abused its discretion in admitting such testimony.” The stated reason is reviewability: without findings it is impossible on appeal to tell whether the court reviewed the proffer or “simply made an off-the-cuff decision.” How strictly other circuits enforce an equivalent findings requirement is not uniform.

General Electric Co. v. Joiner, 522 U.S. 136 (1997), holds that abuse of discretion is the standard for reviewing a decision to admit or exclude expert evidence, and Kumho Tire extends that standard to the trial court's choices about how to test reliability. Both directions of that rule matter to a proponent. An admission supported by element-by-element findings is difficult to disturb. So is an exclusion. That asymmetry of remedy — argue it once, in the district court, on a complete record — is the practical reason the admissibility showing is worth building before it is challenged.

Source text for the rule and both Committee notes: Federal Rule of Evidence 702, Legal Information Institute.

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Published 2026-08-12