Daubert vs. Frye: The Two Standards for Admitting Expert Testimony

Daubert and Frye differ in what the court tests: Daubert tests the reliability of the expert's method and its fit to the case, while Frye tests whether the relevant field has accepted the method. Under Daubert v. Merrell Dow Pharmaceuticals, Inc. (1993), which governs federal trials, the trial judge acts as a gatekeeper and must ensure that the testimony "both rests on a reliable foundation and is relevant to the task at hand." Under Frye v. United States (1923), the older test, the principle or discovery an opinion is deduced from "must be sufficiently established to have gained general acceptance in the particular field in which it belongs."

The tests also differ in three practical ways. Who judges reliability: under Daubert the trial judge assesses the method at the outset, before the jury hears the opinion, while under Frye the court looks to whether the relevant field has accepted it. What the test reaches: Kumho Tire Co. v. Carmichael (1999) held that the Daubert gatekeeping obligation applies to all expert testimony, including testimony based on technical and other specialized knowledge; Frye itself concerned a novel scientific technique, and how far general acceptance reaches is set by each state that keeps it. How flexible it is: the Court called the Daubert inquiry "a flexible one" and kept general acceptance as one consideration among several, where Frye had made general acceptance the exclusive test.

The two tests overlap more than the labels suggest, because a method its field has accepted is easier to defend under either one. They part on two kinds of opinion. A newer method that has been tested and published but is not yet generally accepted can be admitted under Daubert, which held that general acceptance "is not a necessary precondition" to admissibility, but not under Frye. An accepted method applied to too little data can pass Frye's test, which asks about the method, yet be excluded in federal court, because the federal rule on expert testimony requires that the opinion rest on sufficient facts or data and reflect a reliable application of the method to the case. Attorneys are responsible for confirming the governing framework against primary sources.

The Daubert standard is the federal test for admitting expert testimony: the trial judge screens the opinion before the jury hears it and admits it only if its reasoning and method are reliable and fit the facts of the case. The Supreme Court set it out in Daubert v. Merrell Dow Pharmaceuticals, Inc. (1993), a suit over birth defects alleged to have been caused by a prescription antinausea drug, which began in California state court and was removed to federal court on diversity grounds. The Court held that the Frye test was superseded by the adoption of the Federal Rules of Evidence, and it called general acceptance as the exclusive test an "austere standard, absent from, and incompatible with, the Federal Rules of Evidence" that "should not be applied in federal trials."

The Court named considerations that bear on the inquiry: whether the theory or technique can be, and has been, tested; whether it has been peer reviewed and published; its known or potential rate of error; whether standards controlling its operation exist and are maintained; and general acceptance, which "can yet have a bearing on the inquiry." The focus, the Court said, is on principles and methodology rather than on the conclusions they generate, though General Electric Co. v. Joiner (1997) added that conclusions and methodology are not entirely distinct from one another. Kumho Tire Co. v. Carmichael (1999) gave the trial judge the same broad latitude in deciding how to test reliability as in deciding whether the testimony is reliable, so the factors are applied where they are reasonable measures of the reliability of the testimony at hand.

The Court also answered the concern that dropping general acceptance as the exclusive test would let unreliable science reach juries: "Vigorous cross-examination, presentation of contrary evidence, and careful instruction on the burden of proof are the traditional and appropriate means of attacking shaky but admissible evidence." It acknowledged in the same opinion that a gatekeeping role for the judge, however flexible, will on occasion keep authentic insights and innovations from a jury.

In federal court the gatekeeping standard is now written into the federal rule on expert testimony. The rule was amended in 2000 in response to Daubert and the cases applying it, including Kumho, and its committee note says the amendment affirms the trial court's role as gatekeeper while making no attempt to codify the specific Daubert factors. It was amended again in 2023 to clarify and emphasize that expert testimony may not be admitted unless the proponent shows the court that it is more likely than not that the testimony meets the rule's requirements, and to emphasize that each opinion must stay within what a reliable application of the expert's basis and method can support. The 2023 note calls rulings that treated the sufficiency of an expert's basis and the application of the method as questions of weight, not admissibility, an incorrect application of the rules, and it adds that once the court finds the requirements met, any further attack goes to the weight of the evidence. The guide to when a case needs an expert witness lists the rule's requirements.

The Frye standard admits expert testimony only if the principle or method it rests on is generally accepted in the relevant field. It comes from Frye v. United States (1923), in which the Court of Appeals of the District of Columbia affirmed a murder conviction after the trial court had excluded the defense's expert testimony about a systolic blood pressure deception test. The point at which a scientific principle crosses from the experimental to the demonstrable is, the court wrote, difficult to define, and "while courts will go a long way in admitting expert testimony deduced from a well-recognized scientific principle or discovery, the thing from which the deduction is made must be sufficiently established to have gained general acceptance in the particular field in which it belongs." It found that the deception test had not yet gained that standing among physiological and psychological authorities.

In the Supreme Court's account in 1993, general acceptance had been the dominant standard for determining the admissibility of novel scientific evidence at trial in the 70 years since Frye, and the Frye decision itself had focused exclusively on novel scientific techniques. Daubert ended its use in federal trials. A state remains free to keep it, and some do, as the next section shows.

Each state chooses its own standard, because Daubert decided only what governs federal trials. Pennsylvania keeps general acceptance by rule: the Pennsylvania rule on expert testimony requires that "the expert's methodology is generally accepted in the relevant field," and the comment printed with it says the rule reflects Pennsylvania's adoption of the standard in Frye, applies the general acceptance test to "scientific, technical, or other specialized knowledge testimony" and "rejects the federal test derived from Daubert." Massachusetts allows either route: the note to the expert testimony section of its Guide to Evidence describes two ways a judge may find a method reliable, general acceptance in the relevant scientific community, which the note calls the Frye test, or a reliability analysis of the kind Daubert describes, and it says the principal difference from the federal rules is that in Massachusetts general acceptance alone can establish reliability (Massachusetts Court System, Trial Court Law Libraries, 2026). The Massachusetts admissibility guide sets out that standard requirement by requirement.

Because the standards differ, the same report may be admitted without a hearing in one forum and be the subject of a pretrial motion in another, and a case removed from state court is decided under the federal standard, as Daubert itself was. The safe course is to prepare every opinion for both tests: a published method its field has accepted, set out on the page with its sources, the data behind each figure and the reasoning from that data to the conclusion. Attorneys confirm the current rule for their state and forum.

For a vocational, economic or life care opinion, neither test is usually about whether the discipline itself is legitimate; the two differ in how far they look into the particular opinion. Vocational assessment, forensic economics and life care planning each rest on published methods and public data, and Kumho Tire Co. v. Carmichael (1999) described the object of the gatekeeping requirement as making certain that an expert, whether basing testimony on professional studies or personal experience, employs in the courtroom the same level of intellectual rigor that characterizes practice in the field. A gatekeeping court therefore asks about the particular opinion: whether the expert used the method the field uses, whether the data behind it was sufficient, and whether the reasoning from data to conclusion holds together. General Electric Co. v. Joiner (1997) put the last point directly: a court may conclude that there is simply too great an analytical gap between the data and the opinion, even where the method is sound in the abstract.

Under a general-acceptance test the question narrows to the method. A transferable skills analysis, a present value calculation or a life care plan built on treating recommendations follows methods its discipline publishes, so a challenge in that forum more often turns to qualification, to the foundation the expert had and to the weight the jury should give the figures. In federal court, whether a discount rate or an occupational classification has a sufficient basis can be argued to the judge on a pretrial motion, because the 2023 note to the federal rule treats the sufficiency of an expert's basis and the application of the method as questions of admissibility; once the judge finds the requirements met, what remains goes to weight and to cross-examination.

A Daubert challenge to a vocational, economic or life care report usually targets the inputs and their foundation rather than the discipline's method: the restrictions, labor market evidence and occupational coding behind a vocational opinion, the worklife, growth, discount, fringe benefit and consumption inputs of an economic one, and the medical foundation for each item of a life care plan. A challenge to a vocational opinion tends to name one of those three targets. The first is the restriction set: an expert who applied restrictions the medical record does not contain, or who resolved a conflict between treating providers without saying so, has an opinion that does not fit the facts. The second is the labor market: an opinion that names occupations without showing that they exist in hireable form where the person lives, or that relies on a wage source without stating its area and date, is attacked as unsupported by sufficient data. The third is the classification step, where the expert coded the person's past work and the alternative occupations; the objection is that the coding was not done, or was done in a way the published references do not support.

Economic opinions draw challenges to inputs more than to arithmetic: the worklife horizon, the growth and discount assumptions, the treatment of fringe benefits and, in death cases, the personal consumption deduction. The court's question is whether each input has a published basis the expert can point to and whether the expert can explain why that source fits this person. Life care plans draw challenges to foundation: an item priced and projected without a physician or other qualified recommendation behind it, or a frequency and duration that no treating record or literature supports, is the usual target. In each discipline the report that survives is the one that shows its sources, states its assumptions and records the alternatives it considered; the federal and state admissibility guide lists the report elements a challenge examines, discipline by discipline.

Kincaid Wolstein Vocational and Rehabilitation Services (KWVRS) writes its vocational evaluations and life care plans to both tests, on methods their disciplines publish, for plaintiff and defense counsel alike, whichever forum the case is in. KWVRS provides forensic economic analysis with its affiliated firm, Kincaid Wolstein Economics.