The 5 Daubert factors are testability, peer review and publication, known or potential error rate, standards controlling the technique’s operation, and general acceptance within the relevant scientific community. Federal courts use them to decide whether expert testimony is reliable enough for a jury to hear. They come from the Supreme Court’s 1993 decision in Daubert v. Merrell Dow Pharmaceuticals, Inc., which put trial judges in the role of gatekeeper for expert evidence. The Court was explicit that the five are flexible guideposts, not a rigid checklist, and how each one works in practice is often the difference between testimony that gets in and testimony that gets thrown out.
Where the Factors Come From
Before 1993, federal courts screened scientific testimony under the Frye standard, which asked one question: had the method gained general acceptance in its field? In Daubert, the Supreme Court held that the Federal Rules of Evidence, not Frye, control admissibility, and it assigned trial judges the job of ensuring expert testimony rests on a reliable foundation and fits the case.1Justia U.S. Supreme Court Center. Daubert v. Merrell Dow Pharmaceuticals, Inc.
The rule behind the gatekeeping role is Federal Rule of Evidence 702, amended effective December 1, 2023, to clarify that the party offering the expert must show “it is more likely than not” that the testimony will help the jury, is based on sufficient facts or data, is the product of reliable principles and methods, and reflects a reliable application of those methods to the facts.2United States Courts. Federal Rules of Evidence – Rule 702 The 2023 language makes the burden of proof explicit and stops courts from deferring the reliability question to the jury.
In 1999, the Court extended Daubert beyond pure science. Kumho Tire Co. v. Carmichael held that Rule 702 draws no relevant distinction between scientific, technical, or other specialized knowledge, so a tire failure analyst, an accountant, or a vocational expert faces the same scrutiny as a DNA scientist.3Legal Information Institute. Kumho Tire Co. v. Carmichael
Factor 1: Testability
The first factor asks whether the expert’s theory or technique can be tested, and whether it actually has been. It separates science from speculation. A method that cannot be tested gives a court no way to evaluate whether it works. The Supreme Court framed this in classic terms: form a hypothesis, then run experiments to prove or disprove it.4Legal Information Institute. Daubert v. Merrell Dow Pharmaceuticals, Inc.
The expert does not have to have done the testing personally. The question is whether the methodology is the kind that lends itself to empirical verification. A forensic technique validated through controlled studies sits on much stronger ground than one built on personal experience or intuition. When an expert cannot explain how their method could be tested at all, judges treat that as a serious problem.
Factor 2: Peer Review and Publication
The second factor looks at whether the technique has been subjected to peer review and published in a reputable journal. Peer review works as a quality filter. Other experts in the field examine the methodology, check the reasoning, and flag weaknesses before the work reaches a wider audience. Publication signals the work has cleared at least a baseline credibility threshold.
Peer review is not an absolute requirement. Some research is too new or too specialized to have been published, and that alone does not make it unreliable.1Justia U.S. Supreme Court Center. Daubert v. Merrell Dow Pharmaceuticals, Inc. Courts treat this as one indicator among several. An unpublished method that scores well on testability, error rate, and controlling standards can still be admitted, and publication alone will not save a method that is otherwise flawed.
Factor 3: Known or Potential Error Rate
The third factor examines how often a technique produces incorrect results. Every method has some margin of error, and courts want to know what that margin looks like. A DNA analysis with a false-positive rate of one in several billion paints a very different picture than a field test with a 30 percent error rate.
A precise numerical rate is not always required. Federal judges frequently assess the method’s quality more broadly, looking at whether the expert acknowledged limitations, followed proper procedures, and used appropriate controls. A detailed qualitative analysis can satisfy this factor when strict numerical error rates are unavailable. But when an expert has no idea how often their method gets it wrong and offers no framework for estimating accuracy, that silence tells a judge a great deal.5National Institute of Justice. Informing the Daubert Known Error Rate Criterion for DNA Evidence Interpreted Using Probabilistic Genotyping
Factor 4: Standards Controlling the Technique
The fourth factor asks whether established protocols, guidelines, or quality controls govern how the technique is applied. Even a reliable method can produce unreliable results if it is applied inconsistently or without proper controls. This factor gets at the difference between a technique that exists in a vacuum of the expert’s own making and one embedded in a professional framework with defined procedures.
A breathalyzer is a well-accepted tool, but the reading is only trustworthy if the device was calibrated, the operator was trained, and the test followed established protocol. The same logic applies to any expert methodology. Courts look for evidence that the expert followed recognized procedures and that those procedures are maintained and enforced within the relevant professional community.6National Institute of Justice. Law 101 – Legal Guide for the Forensic Expert – Daubert and Kumho Decisions
Factor 5: General Acceptance
The fifth factor is whether the theory or technique has gained widespread acceptance in the relevant scientific community. This was the only factor under Frye. Under Daubert it is one piece of a larger puzzle.1Justia U.S. Supreme Court Center. Daubert v. Merrell Dow Pharmaceuticals, Inc. General acceptance still carries real weight, especially for well-established fields. If most toxicologists endorse a particular methodology for determining causation, that consensus matters.
Newer techniques are where this factor gets interesting. A cutting-edge method may have strong testability, a known error rate, and published peer-reviewed studies while still lacking broad acceptance because the field is still evaluating it. Under Daubert, that method can be admitted anyway. The Court deliberately moved away from letting general acceptance serve as a veto, recognizing that valid techniques sometimes arrive before consensus does.
How the Five Factors Work Together
Daubert is often misread as a scorecard. The Supreme Court was emphatic on the opposite point: “We do not presume to set out a definitive checklist or test.” The inquiry is “a flexible one,” and its focus must be on principles and methodology, not on the conclusions the expert reaches.4Legal Information Institute. Daubert v. Merrell Dow Pharmaceuticals, Inc. Not every factor will apply in every case, and judges may consider factors the Court did not list.
Failing on one factor is not automatically fatal. An expert whose method has no peer-reviewed publication but scores well on testability, error rate, and controlling standards can still get through the gate. Judges also have room to weigh the factors differently depending on the type of expertise. The gatekeeping analysis for an epidemiologist looks different from the analysis for a construction defect expert, and Kumho Tire confirmed that trial judges have the same broad latitude to decide which Daubert factors are reasonable to apply in any given case.3Legal Information Institute. Kumho Tire Co. v. Carmichael
What Happens When an Expert Fails a Daubert Challenge
When one side wants to keep the other side’s expert off the stand, the usual vehicle is a motion in limine filed after discovery closes, once the challenging party has reviewed the expert’s report and deposition. If the judge decides a hearing is warranted, the court holds a Daubert hearing where the expert may testify, both sides argue the methodology, and the judge evaluates the testimony against the Daubert factors and Rule 702. The judge can admit the testimony, exclude it entirely, or limit its scope. Credentials alone will not carry the day. The judge is evaluating the soundness of the method, not the résumé.
Losing this fight can end a case. In toxic tort, medical malpractice, and products liability litigation, expert testimony is often the only way to prove an essential element such as causation. If the court excludes the plaintiff’s expert, the plaintiff often cannot prove the case at all, the defendant moves for summary judgment on the ground that no admissible expert evidence supports the claim, and courts regularly grant those motions.
Not Every Court Applies Daubert
Daubert governs in all federal courts and roughly two-thirds of state courts. A handful of states still follow Frye, which focuses only on general acceptance. Notable Frye states include California, New York, Illinois, Pennsylvania, and Washington. Several other states apply hybrid or state-specific tests that borrow from both frameworks.
The difference matters. Under Frye, a novel but well-tested technique may be excluded because the scientific community has not broadly adopted it yet. Under Daubert, that same technique can come in if the judge finds the methodology reliable across the full range of factors. If you are involved in litigation, the first question is whether the case is in federal or state court, and if state court, which standard applies. The answer shapes how expert testimony is prepared, challenged, and defended.