I don't think we ever did a post on this, but back in 2023, Federal Rule of Evidence 702 was amended to clarify that the burden of showing admissibility of an expert witness's testimony falls on the offering party (addition highlighted below):
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 . . .
FRE 702 (2025).
T his is consistent with a long-standing Third Circuit holding in In re Paoli R.R. Yard Pcb Litig., 35 F.3d 717, 744 (3d Cir. 1994):
"[I]t is plain that the proponent must make more than a prima facie showing . . . that a technique is reliable." . . . This does not mean that plaintiffs have to prove their case twice -- they 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.
We saw the effect of this last week in Agilent Technologies, Inc. v. Axion BioSystems, Inc., C.A. No. 23-198, D.I. 550 (D. Del. Mar. 19, 2026), when the Court granted a Daubert motion after the plaintiff seemingly flubbed the burden analysis.
In a patent action, the plaintiff had offered damages testimony regarding a method claim, but their expert had not apportioned damages to account for what proportion of the defendant's sales actually result in infringement. The defendant sought to exclude the testimony based on a claim that not every use of the product practices the method.
The plaintiff responded by saying that the defendant had failed to show that some uses of the product don't infringe. The Court rejected that argument, holding that it is the plaintiff's burden, as the party offering the expert, to show prove that the expert's testimony is admissible:
Plaintiff’s arguments are not convincing. As an initial matter, in criticizing Defendant for failing to point to evidence regarding the typical use of the accused products (which, incidentally, seems to ignore Defendant’s reliance on Dr. Frazier’s contributory infringement opinions), Plaintiff loses sight of the fact that Defendant does not carry the burden here. . . . Rather, it is the plaintiff’s burden to demonstrate by a preponderance of the evidence that its expert’s opinions are reliable, see, e.g., Sec’y U.S. Dep’t of Lab. v. Nursing Home Care Mgmt. Inc., 128 F.4th 146, 162 (3d Cir. 2025); In re Paoli R.R. Yard PCB Litig., 35 F.3d 717, 744 (3d Cir. 1994), and that its expert’s damages opinion limited damages to products that were actually used to perform the claimed method . . . .
Agilent Technologies, Inc. v. Axion BioSystems, Inc., C.A. No. 23-198, D.I. 550 (D. Del. Mar. 19, 2026).
The Court ultimately granted the Daubert motion and struck the testimony. Just something to keep in mind for the next time you find yourself briefing a Daubert motion. . . .
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