In Daubert v. Merrell Dow Pharmaceuticals, Inc., decided in 1993, the U.S. Supreme Court threw out the seventy-year-old “general acceptance” test for expert testimony and replaced it with a flexible reliability inquiry run by the trial judge. Every federal judge became a gatekeeper, responsible for screening expert evidence for both relevance and methodological soundness before a jury ever hears it. Two follow-up rulings and a 2023 amendment to the Federal Rules of Evidence have sharpened that role, and the framework now governs expert testimony in federal court and in roughly two-thirds of state courts.
The Dispute That Reached the Supreme Court
The case grew out of birth-defect lawsuits brought by two families who blamed Bendectin, a prescription anti-nausea drug taken during pregnancy, for their children’s injuries.1Justia. Daubert v. Merrell Dow Pharmaceuticals, Inc. Merrell Dow, the manufacturer, pointed to an extensive body of peer-reviewed research finding no link between the drug and birth defects. Its expert relied on that published literature.
The plaintiffs offered eight experts of their own. Their opinions drew on animal studies, analyses of Bendectin’s chemical structure, and a reanalysis of previously published human data. That reanalysis had never been published or peer reviewed. Applying the older Frye “general acceptance” test, the trial court excluded the plaintiffs’ evidence and granted summary judgment for Merrell Dow. The Ninth Circuit affirmed, noting the evidence appeared to have been developed for the litigation itself.1Justia. Daubert v. Merrell Dow Pharmaceuticals, Inc. Without their experts, the families had no case, so they took the admissibility question to the Supreme Court.
What the Court Held
The Court ruled unanimously that the Frye standard had been superseded when Congress adopted the Federal Rules of Evidence in 1975. Writing for the majority, Justice Blackmun held that nothing in those rules committed federal courts to a single admissibility test. Chief Justice Rehnquist, joined by Justice Stevens, concurred in part but worried the majority’s framework gave judges too little concrete direction.1Justia. Daubert v. Merrell Dow Pharmaceuticals, Inc.
The heart of the decision is the gatekeeping duty. Federal trial judges must ensure that expert testimony is both relevant to a fact in dispute and grounded in reliable methodology. The Court told judges to focus on the expert’s principles and methods, not on the conclusions those methods produced. An expert can reach a surprising result, but the reasoning that got there has to be scientifically defensible.
The Factors Judges Weigh
Instead of a checklist, the Court set out several factors a judge may consider when evaluating reliability:1Justia. Daubert v. Merrell Dow Pharmaceuticals, Inc.
- Whether the theory or technique can be tested and potentially disproven.
- Whether the work has been subjected to peer review and publication.
- The known or potential rate of error for the technique.
- The existence and maintenance of standards controlling the technique’s operation.
- Whether the method is generally accepted in the relevant scientific community. This is the old Frye factor, now one input among several rather than the whole test.
No single factor decides the question, and judges do not have to apply all of them in every case. The inquiry is meant to bend to the type of expertise at issue.
The Rule Daubert Replaced
The prior standard came from Frye v. United States, a 1923 federal appellate case involving an early precursor to the polygraph. That court refused to admit results from a systolic blood pressure deception test, holding that a scientific technique is admissible only once it has “gained general acceptance in the particular field in which it belongs.”2H2O. Frye v. United States For seventy years, that one sentence controlled expert admissibility in most American courts. The judge’s job was essentially to poll the relevant field. New or unconventional science could be excluded even when it looked promising, and long-standing methods could pass through because they always had.
How the Framework Was Completed
The original opinion left open questions that two later Supreme Court decisions resolved. The three cases together are commonly called the Daubert trilogy.
General Electric Co. v. Joiner (1997)
In Joiner, the Court held that appellate courts should review a trial judge’s admissibility ruling under an abuse-of-discretion standard. An appeals court will not reverse unless the ruling was clearly unreasonable.3Justia. General Electric Co. v. Joiner That gives trial judges wide latitude, and it means the same expert testimony can be admitted in one courtroom and excluded in another without either ruling being disturbed.
Kumho Tire Co. v. Carmichael (1999)
The original opinion focused on scientific testimony, leaving open whether the gatekeeping duty extended to experts who rely on technical skill or practical experience. In Kumho Tire, a case about a tire-failure analyst who worked from visual inspection and professional experience rather than peer-reviewed studies, the Court answered yes. Gatekeeping applies to all expert testimony.4Justia. Kumho Tire Co. v. Carmichael The Court also reiterated that the specific Daubert factors are a flexible toolkit. Some will matter more than others depending on the field.
The 2023 Amendment to Rule 702
Federal Rule of Evidence 702 codifies the gatekeeping framework. On December 1, 2023, an amendment took effect that wrote the preponderance-of-the-evidence standard directly into the rule. The party offering expert testimony must now show the court “that it is more likely than not” the testimony meets each admissibility requirement.5Legal Information Institute. Federal Rules of Evidence Rule 702 – Testimony by Expert Witnesses
The advisory committee behind the change noted that many courts had been treating questions about the sufficiency of an expert’s data and the reliability of the methods as issues of weight for the jury rather than threshold admissibility questions for the judge. The committee called that an incorrect application of the rule. The amendment makes clear that judges must actually evaluate reliability before letting testimony in.6H2O. 2023 Changes to Rule 702 and Related Advisory Committee Notes
Federal Rule, State Variations
Daubert governs every federal court, but each state chooses its own standard in state-court proceedings. Roughly two-thirds of states have adopted the Daubert framework or something close to it. A smaller group still follows the Frye general-acceptance test, and the holdouts include some of the most populous jurisdictions: California, New York, Illinois, Pennsylvania, and Washington. A few other states use hybrid approaches that map onto neither framework cleanly.
The split has real consequences. The same expert can be admissible in a federal courthouse and excluded in a state courthouse across the street. An expert whose methodology is cutting-edge but not yet broadly adopted has a better chance under Daubert, where the judge weighs multiple reliability factors. In a Frye state, that same expert may be shut out because the technique has not yet won consensus.
Why the Ruling Still Matters
The most visible consequence of the framework is the Daubert hearing, a pretrial proceeding at which the judge decides whether a specific expert’s testimony gets in. Either side can move to exclude the other’s expert, usually after discovery closes and each side has the other’s expert report and deposition in hand.7National Institute of Justice. Daubert and Kumho Decisions The judge evaluates the expert’s qualifications, the reliability of the methodology, and whether the testimony fits the facts. The proponent carries the burden by a preponderance of the evidence.5Legal Information Institute. Federal Rules of Evidence Rule 702 – Testimony by Expert Witnesses
In toxic tort, pharmaceutical, and product liability cases, the plaintiff typically needs an expert to prove that the defendant’s product caused the injury. Exclude that expert and the plaintiff usually has no case, which is exactly what happened to the families in Daubert itself. A single admissibility ruling can determine whether a multimillion-dollar case reaches a jury or ends on summary judgment. The 2023 amendment reinforced that dynamic by telling judges they cannot hand reliability questions off to the jury. The trend over three decades has been toward more rigorous gatekeeping, not less.