Expert Testimony Admissibility: Reliability and General-Acceptance Frameworks

Every court that hears expert testimony asks a threshold question before the jury hears the opinion: is this the kind of evidence a factfinder should be allowed to weigh? Two families of answer are in use. The first, adopted for the federal courts in Daubert v. Merrell Dow Pharmaceuticals, Inc. (1993) and since followed in most states, makes the trial judge a gatekeeper who examines the reliability of the expert's method and its fit to the facts of the case. The second and older family, associated with Frye v. United States (1923), asks one question, whether the method is generally accepted in the relevant professional or scientific community, and leaves the rest to cross-examination and to the weight the jury gives the testimony.

The two families overlap more than the labels suggest. General acceptance is one of the considerations a gatekeeping court weighs, and a general-acceptance court still requires the witness to be qualified and the method to be applied to the case at hand. Where they part is on a novel or contested method: a gatekeeping court can exclude an accepted method that was applied carelessly, or admit a newer method that has been tested and published, while a general-acceptance court looks to the field's consensus and stops there. Attorneys are responsible for confirming the governing framework against primary sources; the label a state uses is not always a reliable guide to how its courts apply it.

For the disciplines KWVRS practices, the gatekeeping inquiry is rarely about whether the discipline itself is legitimate. Vocational assessment, forensic economics and life care planning each rest on published methods and public data, and Kumho Tire Co. v. Carmichael (1999) confirmed that the same reliability inquiry reaches technical and experience-based experts, not only laboratory science. The questions a gatekeeping court asks are therefore 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 exclude an opinion when the gap between the data and the conclusion is too wide, even where the method is sound in the abstract.

Under a general-acceptance framework the inquiry narrows to the method. A transferable skills analysis, a present value calculation or a life care plan built on treating recommendations is an accepted method, so the challenge usually shifts to qualification, to the foundation the expert had, and to the weight the jury should give the figures. The practical difference for counsel is where the argument is made: in a gatekeeping forum the dispute about a discount rate or an occupational classification is a pretrial motion; in a general-acceptance forum it is more often a cross-examination.

A challenge to a vocational opinion tends to name one of 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 admissibility framework does not change because the expert testifies by video. What changes is the mechanics of foundation: the exhibits the expert relies on must be in front of the court and opposing counsel in the same form, the expert must be able to identify the records reviewed without a paper file at hand, and any demonstrative the opinion depends on has to be admitted through the same process as at a live hearing. Counsel who intend to present an expert remotely confirm the forum's practice for exhibits and for the oath in advance, because a foundation gap at a remote hearing is harder to cure on the spot.

State courts vary in three ways that matter to preparation. Some apply a gatekeeping framework in name but rely on the general-acceptance question in practice; some apply a general-acceptance framework to scientific evidence and a different test to technical or experience-based opinions; and a number have written their own factors into an evidence rule or a leading decision. The same report may therefore be admitted without a hearing in one forum and be the subject of a pretrial motion in the neighboring one. The safe course, and the one KWVRS reports are written to, is to prepare every opinion so that it satisfies the more demanding gatekeeping inquiry: identified sources, a stated method, the data behind each figure, and the reasoning from that data to the conclusion set out on the page.