A Daubert challenge is a pretrial motion asking a federal judge to block an opposing party’s expert witness from testifying because the expert’s methods, data, or reasoning fail the reliability and relevance standards set by Federal Rule of Evidence 702. The motion takes its name from the Supreme Court’s 1993 decision in Daubert v. Merrell Dow Pharmaceuticals, which made trial judges the gatekeepers of expert evidence.1Cornell Law Institute. Daubert v. Merrell Dow Pharmaceuticals, 509 US 579 (1993) Because many cases turn on what an expert is allowed to tell the jury, a successful Daubert motion can end a lawsuit before it ever reaches trial.
The Standard a Judge Applies
Rule 702 is the yardstick. As amended effective December 1, 2023, it lets a qualified expert testify only if the party offering the testimony shows it is “more likely than not” that four conditions are met:
- The expert’s specialized knowledge will help the jury understand the evidence or resolve a factual dispute.
- The testimony rests on sufficient facts or data.
- The testimony is the product of reliable principles and methods.
- The expert applied those methods reliably to the facts of the case.
The “more likely than not” language was the key change in the 2023 amendment.2United States Courts. Federal Rules of Evidence Before the revision, some federal courts treated expert testimony as presumptively admissible and left reliability disputes for cross-examination. The amended rule puts the judge, not the jury, in charge of screening reliability by a preponderance of the evidence. That shift gave judges more confidence to exclude weak expert opinions and gave litigants firmer ground for filing these motions.
One thing the standard does not ask: whether the expert’s conclusion is right. The judge is not choosing between competing experts. The question is whether the reasoning is defensible, not whether the answer is correct.
What the Judge Looks At
The Supreme Court identified several non-exclusive factors that guide the reliability inquiry:
- Whether the theory or technique can be tested, and whether anyone has tested it.
- Whether it has been subjected to peer review and publication.
- The known or potential rate of error, and the existence of standards controlling the technique’s use.
- Whether the theory or technique is generally accepted in the relevant field.1Cornell Law Institute. Daubert v. Merrell Dow Pharmaceuticals, 509 US 579 (1993)
No single factor is required, and the list is not exhaustive. General acceptance still matters, but it is no longer the only thing that counts. A newer technique with strong test results and low error rates can pass muster even if the field has not fully embraced it. Judges also have flexibility to weigh the factors differently depending on the type of expertise involved: a challenge to a damages model might focus on the data inputs and error rate, while a challenge to an accident reconstruction expert might center on whether the methodology has been tested in similar conditions.
Qualifications can be attacked too, but this is the least effective angle. Challenges based on methodology succeed far more often than challenges based on credentials alone. A well-credentialed expert using a flawed method is more vulnerable than a less-credentialed expert applying a sound one.
How the Motion Moves Through Court
A Daubert challenge begins with a written motion identifying the specific opinions being challenged and explaining why the expert’s methodology, data, or qualifications fall short of Rule 702. There is no fixed deadline in the federal rules. The date is set by the judge’s scheduling order and varies from case to case, though most scheduling orders place the deadline after expert discovery closes and well before trial.3Legal Information Institute (LII) at Cornell Law School. Rule 16 Pretrial Conferences; Scheduling; Management
Once the motion is filed, the court often holds a Daubert hearing where both sides present arguments. The party who hired the expert carries the burden of proving admissibility by a preponderance of the evidence.2United States Courts. Federal Rules of Evidence That showing might include live testimony from the expert, deposition excerpts, supporting publications, and competing declarations. Some judges skip the live hearing entirely and rule on the written submissions when the record is clear.
The ruling can go three ways. The judge can admit the testimony, exclude it outright, or limit it — allowing the expert to testify on some subjects but not others. Partial exclusion is more common than most people expect. A damages expert might be permitted to testify about lost profits while being barred from opining on speculative future market growth.
What the Ruling Does to a Case
Losing an expert can be devastating. In medical malpractice, products liability, toxic exposure, and patent disputes, expert testimony is not just helpful but legally required to prove core elements of the claim. If a Daubert ruling knocks out the only expert on causation, the opposing side will almost certainly move for summary judgment, and the court will likely grant it. The case ends without a trial.
Even when exclusion does not directly trigger dismissal, it can force an unfavorable settlement. A plaintiff who loses a damages expert still has a case in theory but no credible way to put a number in front of the jury. That imbalance shifts settlement leverage sharply toward the defendant.
If the challenge fails and the testimony comes in, cross-examination becomes the main tool for weakening the expert at trial. Gaps in the data, weaknesses in the method, and overstatements in the conclusions can all be exposed in front of the jury. The trade-off is that the jury, not the judge, then decides how much weight the testimony deserves.
Whether the Ruling Can Be Appealed
Daubert rulings generally cannot be appealed right away. A ruling on expert testimony is not one of the narrow categories of orders eligible for immediate appeal in federal court.4Office of the Law Revision Counsel. 28 US Code 1292 – Interlocutory Decisions The losing party usually has to wait for a final judgment and then raise the issue on appeal. A trial court can occasionally certify a Daubert ruling for interlocutory review when it involves a controlling legal question with substantial disagreement, but that path is uncommon.
On appeal, the standard of review is abuse of discretion. The appellate court will overturn the trial judge only if the ruling was clearly unreasonable, not merely because the appellate panel would have decided differently.5Law.Cornell.Edu. General Electric Co v Joiner Successful Daubert appeals are rare, which is why getting the motion right at the trial level matters so much.
State Courts Are Not All the Same
Daubert governs federal court, and roughly 38 states have adopted it as well. A handful of states, including California, New York, Pennsylvania, Illinois, and Washington, still apply some version of the older Frye “general acceptance” test, which asks primarily whether the expert’s method is generally accepted in the relevant scientific community.6Legal Information Institute (LII) / Cornell Law School. Frye Standard A newer technique with strong test results but limited adoption might survive under Daubert and fail under Frye. If a case is in state court, confirming which standard applies is the first step in planning any challenge to expert evidence, because the strategy under each standard looks quite different.