Support Our Work
Support Our Work

6.6 Expert Testimony

Updated 2014 by Alice Nelson

When planning a case, attorneys should determine early on whether an expert will be needed. Generally, an expert is helpful or even necessary when the facts and issues of the case are not easily understandable. For example, most cases under the Individuals with Disabilities Education Act need one or more experts to explain the child’s progress or lack thereof or the behavioral interventions that should have been used by school personnel.1 Experts are used in a wide variety of circumstances.2

Rule 26 of the Federal Rules of Civil Procedure identifies two types of experts: trial experts (Fed. R. Civ. P. 26(a)(2)) and consultant experts, those employed but not expected to testify (id. 26(a)(4)(D)). Trial experts are discussed below. Consultant experts are not discussed further here.

As with every other aspect of trial advocacy, careful preparation is required. The attorney must try to learn as much as the expert knows in the subject matter of the expert’s opinion. The attorney’s job is to make sure that the expert’s report and testimony are in language that is understandable to the trier of fact. The language may be a bit more sophisticated if the trier of fact is a district court. The expert must understand the theory of the case and how the expert’s opinion fits in. Consider visual aids including demonstrative evidence that might assist.3

6.6.A. Daubert

Daubert v. Merrill Dow Pharmaceuticals began a revolution in federal expert witness practice by greatly expanding the power of federal courts to exclude or limit expert testimony.4 Before Daubert, trial judges largely confined admissibility determinations to qualifications. The proponent bore the burden to demonstrate that the expert was qualified through education, knowledge, experience, skill, or training to render an expert opinion. Daubert expanded the “gatekeeping function.”5 It held that, in addition to determining whether an expert is qualified to testify on the matters proposed to be addressed, a court must determine whether the expert’s methodology is sufficiently reliable to support the proposed opinions. The court must further decide whether the expert’s proposed testimony will, through the application of scientific, technical, or specialized expertise, assist the trier of fact in understanding the evidence or determining a fact at issue.6 Daubert arose from a dispute over scientific expert testimony, and Kumho Tire Company v. Carmichael subsequently expanded its holding to the admissibility of all nonscientific expert testimony.7 In 2000 Federal Rule of Evidence 702 was revised essentially to codify Daubert:

If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise, if (1) the testimony is based upon sufficient facts or data, (2) the testimony is the product of reliable principles and methods, and (3) the witness has applied the principles and methods reliably to the facts of the case.8

Before admitting expert testimony, a district court must determine whether the expert is qualified by knowledge, skill, experience, training, or education to render an opinion, and it must satisfy itself that the proposed expert testimony is both reliable and relevant, in that it will assist the trier of fact, before permitting the jury to assess such testimony.9 A district court’s decision as to the admissibility of the evidence, whether it is admitted or not, is reviewed under the “abuse of discretion” standard.10

6.6.B. Qualifications

Qualification as an expert does not require a scientific background. Expert status may be based on extensive experience, knowledge, skill, or on-the-job training, even in the absence of formal scientific education.11 Moreover, “it is an abuse of discretion for a trial court to exclude expert testimony solely on the ground that the witness is not qualified to render an opinion because the witness lacks expertise in specialized areas that are directly pertinent to the issues in question, if the witness has educational and experiential qualifications in a general field related to the subject matter of the issue in question.”12 Testimony beyond the expert’s scope of expertise should be excluded.13 Disputes over the strength of qualifications and credentials ordinarily go to the weight to be accorded to expert testimony and not to its admissibility.14 As the Court in Daubert noted, “[v]igorous 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.”15

6.6.C. Reliability Principles and Methods

Daubert requires an inquiry into reliability “to make certain that an expert, whether basing testimony upon professional studies or personal experience, employs in the courtroom the same level of intellectual rigor that characterizes the practice of an expert in the relevant field.”16 Accordingly, Daubert directed that trial courts consider as part of the reliability inquiry for scientific expertise: (1) whether the expert’s theory can and has been tested;17 (2) whether the theory has been subjected to peer review and publication;18 (3) the known or potential rate of error of the particular scientific technique;19 and (4) whether the technique is generally accepted in the scientific community.20 Kumho Tire applied the same criteria to assess the reliability of experience with respect to nonscientific expert testimony.21 The specified factors are guideposts; there is no requirement that a district court consider each of them or that an expert’s testimony must satisfy each of the listed factors.22

Daubert noted that its required reliability inquiry should be “a flexible one.”23 Although Daubert emphasized that “[t]he focus, of course, must be solely on principles and methodology, not on the conclusions that they generate,”24 General Electric Company v. Joiner insisted that “conclusions and methodology are not entirely distinct,”25 thereby expanding the trial court’s authority to exclude proposed testimony as unreliable.

6.6.D. The Fit Between Methods and Conclusions

Joiner expanded the reliability inquiry to include an assessment of the fit between each of the experts’ specific opinions and the data, principles, and methods from which it is purportedly derived. The Court reasoned that even when an expert uses reliable methods and data, “[a] court may conclude that there is simply too great an analytical gap between the data and the opinion proffered” and that “nothing in either Daubert or the Federal Rules of Evidence requires a district court to admit opinion evidence that is connected to existing data only by the ipse dixit of the expert.”26

In the wake of Joiner, several Section 1983 claims dependent on expert testimony foundered for lack of sufficient fit between the expert’s opinions and underlying data.27 However, when fit can be shown, the court should admit the expert’s opinion, leaving for the jury the question of whether to credit the testimony.28 The Advisory Committee Notes to amended Rule 702 caution that “the trial court’s role as gatekeeper is not intended to serve as a replacement for the adversary system.29

Expert testimony can be crucial to proving causation, and it is particularly likely to trigger reliability and fit objections.30 To qualify as reliable, causation testimony need not negate every alternative hypothesis.31

6.6.E. Reliance upon Other Experts

Experts routinely rely on the work of others; that reliance is not objectionable as hearsay.32 Federal Rule of Evidence 703 specifically provides: “An expert may base an opinion on facts or data in the case that the expert has been made aware of or personally observed.” If experts in the particular field would reasonably rely on those kinds of facts or data in forming an opinion on the subject, they need not be admissible for the opinion to be admitted. An expert may rely upon reports of others to formulate his opinion, and such reliance is often an indicia of reliability.33 Similarly, consultation with other experts can be a reliable and appropriate methodology under Daubert.34

Although experts are entitled to base their opinions on facts perceived by or made known to them, testifying experts may be excluded from the courtroom during the testimony of other witnesses under Rule 615 unless their presence is “essential.”35 Generally, if the expert has no firsthand knowledge of the facts, the expert is permitted to remain in the courtroom.36

6.6.F. Will Expert Testimony Assist the Trier of Fact?

Federal Rule of Evidence 702 requires that admissible expert testimony assist the trier of fact. Expert testimony only assists the trier of fact when it addresses “beyond the understanding of the average person.”37 It does not do so when it addresses only matters that counsel can present through closing argument.38 Similarly, expert testimony will not assist the trier of fact by explaining the governing law; that is the responsibility of the court.39 Further, Daubert explained the important interrelationship between Rule 702 and Rule 403: “Expert evidence can be both powerful and quite misleading because of the difficulty in evaluating it. Because of this risk, the judge in weighing possible prejudice against probative force under Rule 403 of the present rules exercises more control over experts than over lay witnesses.”40

6.6.G. Expert Reports

Rule 26(a)(2)(B)(i) of the Federal Rules of Civil Procedure requires parties to disclose the names of their retained trial experts before trial and to give the opposing party a written report, prepared and signed by the expert witness, that must contain “a complete statement of all opinions the witness will express and the basis and reasons for them.” Parties must also provide “the facts or data considered by the witness in forming them,” exhibits, the expert’s qualifications (including publications) and compensation, and a listing of expert testimony during the preceding four years.41 The report should be sufficiently comprehensive to establish admissibility under all of the Rule 702 criteria.42

Over the years, the rules have changed regarding the disclosure of communications between counsel and the expert. In 2010, Rule 26 was amended to provide that such communications are not discoverable and that draft reports are protected from disclosure. Not protected are communications regarding the compensation of the expert, the identification of the facts or data that counsel provided and those that the expert considered, and the assumptions that the attorney provided and that the expert relied on in forming the opinions.43

6.6.H. Determining Admissibility of Expert Testimony

The burden of establishing the admissibility of expert testimony rests with its proponent.44 An opposing party can challenge the admissibility of all or part of proposed expert testimony before trial through a motion in limine or through voir dire when the expert is tendered at trial. The volume of reported cases suggests that many, if not most, objections now arise pretrial in motions in limine. Accordingly, the proponent should anticipate and prepare from the outset to overcome a motion in limine, beginning with the preparation of the expert’s report.

In limine motions generally follow an expert’s deposition. Rule 26(b)(4)(A) permits the expert’s deposition but only after the report is provided.45   A trial court has discretion to grant a motion in limine without first conducting an evidentiary hearing if the expert’s report fails to establish one of the elements required for admissibility. Although courts frequently hold evidentiary hearings to resolve in limine motions, often referred to as Daubert hearings, the determination of whether to conduct a Daubert hearing is committed to the discretion of the trial court, and a trial court can grant or exclude an expert’s testimony without first conducting a Daubert hearing.46 As with all evidentiary objections, Daubert objections to the admissibility of an expert’s testimony can be waived by failing to timely raise them in the trial court.

Updated 2014 by Alice Nelson