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

  • 1. Individuals with Disabilities Education Act (IDEA), 20 U.S.C. §§ 1401 et seq. For an example of how an expert might be used in an IDEA case, see G.S. v. Cranbury Township Board of Education, 450 F. App'x 197, 200 (3d Cir. 2011).
  • 2. See, e.g., Air Wisconsin Airlines Corporation v. Hoeper, 134 S. Ct. 852 (2014) (behavioral expert); Koontz v. St. Johns River Water Management District, 133 S. Ct. 2586, 2593 (2013) (property experts); PPL Corporation v. C.I.R., 133 S. Ct. 1897, 1903 (2013) (tax expert); Comcast Corporation v. Behrend, 133 S. Ct. 1426 (2013) (damages expert in class action context).
  • 3. Similarly, preparation for cross-examination requires thorough familiarity with the subject matter and relevant literature, especially anything the expert has written. Review previous testimony and reports by the expert. Consider impeachment by using scientific treatises. See W.E. Shipley, Use of Medical or Other Scientific Treatises in Cross-Examination of Expert Witnesses, 60 A.L.R.2d 77 (2011).
  • 4. Daubert v. Merrell Dow Pharmaceuticals, 509 U.S. 579 (1993).
  • 5. Id. at 589 n.7.
  • 6. The Federal Judicial Center's Reference Manual on Scientific Evidence (3d ed. 2011) is a useful guide to many of these issues.
  • 7. Kumho Tire Company v. Carmichael, 526 U.S. 137 (1999).
  • 8. See generally, Fed. R. Evid. 702 Committee Notes on Rules -- 2000 Amendment.
  • 9. Conroy v. Vilsack, 707 F.3d 1163 (10th Cir. 2013).
  • 10. General Electric Company v. Joiner, 522 U.S. 136, 141 (1997) ("abuse of discretion" standard); 4 Weinstein's Federal Evidence § 702-02 [4]–[5] (2013). However, as in other areas of the law, if the district court applied the incorrect legal standard, then the review is de novo. United States v. Garcia, 635 F.3d 472, 476 (10th Cir. 2011).
  • 11. See, e.g., Quiet Technology DC-8 Incorporated v. Hurel-Dubois UK Limited, 326 F.3d 1333, 1342–43 (11th Cir. 2003) (expert who had worked in field for nearly twenty years, had worked with experts in field, and had extensive on-the-job training was qualified; and distinguishing between reliability and qualifications); see also In re Flashcom Incorporated, 503 B.R. 99, 124 (C.D. Cal. 2013) (Rule 702 "contemplates a broad conception of expert qualifications.").
  • 12. 4 Weinstein's Federal Evidence § 702.04[1][a].
  • 13. Levin v. Dalva Brothers, Inc., 459 F.3d 68, 78–79 (1st Cir. 2006).
  • 14. See Jahn v. Equine Services, PSC, 233 F.3d 382, 393 n.8 (6th Cir. 2000), (citing McCullock v. H.B. Fuller Company, 61 F.3d 1038, 1045 (2d Cir. 1995)). See also Arkansas Game and Fish Commission v. United States, 736 F.3d 1364, 1378 (Fed. Cir. 2013); Harris v. Gourley, No. 1:10-CV-99 (M.D. Ga. March 27, 2013).
  • 15. Daubert, 509 U.S. at 596.
  • 16. Kumho Tire Co. v. Carmichael, 526 U.S. 137, 152 (1999).
  • 17. Daubert, 509 U.S. at 593.
  • 18. Id. at 593–94.
  • 19. Id. at 594.
  • 20. Id.; 4 Weinstein's Federal Evidence § 702.05[2][c].
  • 21. Kumho Tire Co., 526 U.S. at 152.
  • 22. See United States v. Conn, 297 F.3d 548, 556 (7th Cir. 2002) ("Using the Daubert factors as a point of departure, the district court is free to fashion an approach more precisely tailored to an evaluation of the particular evidentiary submission before it."). For a recent application, see Peoples State Bank v. Stifel, Nicolaus and Company, 2013 WL 1024917 (S.D. Ind. March 14, 2013).
  • 23. Daubert, 509 U.S. at 594.
  • 24. Id. at 595.
  • 25. Joiner, 522 U.S. at 146.
  • 26. Id.
  • 27. See, e.g., Nimely v. City of New York, 414 F.3d 381, 399 (2d Cir. 2005) (abuse of discretion to admit expert testimony of "misperception hypothesis" as explanation for variance between police officer perception and physical evidence in excessive force wrongful shooting claim); Burleson v. Texas Department of Criminal Justice, 393 F.3d 577 (5th Cir. 2004) (expert witness properly excluded in Eighth Amendment claim that defendants exposed plaintiffs to hazardous conditions as prison welder causing him to develop radiation-induced cancer; no reliable methodology supported expert's claim of harmful exposure level); McDowell v. Brown, 392 F.3d 1283 (11th Cir. 2004) (plaintiff's expert witness properly excluded in claim by inmate that 4-hour delay in treating spinal epidural abscess caused or worsened resulting paralysis since studies only explored effects of 48-hour or longer delays; expert's causation conclusion was therefore unreliable assertion). See also Fitzgerald v. Corrections Corporation of America, 403 F.3d 1134 (10th Cir. 2005) (holding inadmissible affidavit submitted by defense expert physician in support of summary judgment attesting to quality care offered by defendant physician; affidavit offered no factual foundation for its conclusion).
  • 28. See Smith v. Ford Motor Company, 215 F.3d 713, 718 (7th Cir. 2000) ("The soundness of the factual underpinnings of the expert's analysis and the correctness of the expert's conclusions based on that analysis are factual matters to be determined by the trier of fact ...."). The proponent of the expert testimony need not demonstrate that the testimony is correct—only that the expert is qualified and that his testimony is based on reliable methodology. "[I]t is not the role of the district court to make ultimate conclusions as to the persuasiveness of the proffered evidence." Quiet Technology DC-8, 326 F.3d at 1341. "[A] district court's gatekeeper role under Daubert 'is not intended to supplant the adversary system or the role of the jury.'" Id. (quoting Maiz v. Virani, 253 F.3d 641, 666 (11th Cir. 2001)). See also Fed. R. Evid. 702 Committee Notes on Rules -- 2000 Amendments ("The emphasis in the amendment on 'sufficient facts or data' is not intended to authorize a trial court to exclude an expert's testimony on the ground that the court believes one version of the facts and not the other.").
  • 29. Fed. R. Evid. 702 Committee Notes on Rules -- 2000 Amendments (quoting United States v. 14.38 Acres of Land, 80 F.3d 1074, 1078 (5th Cir. 1996)).
  • 30. Compare Brown v. Illinois Central Railroad Company, 705 F.3d 531, 535–38 (5th Cir. 2013) (expert failed to articulate reliable methodology), with In re Flonase Antitrust Litigation, 907 F. Supp. 2d 637, 645  (E.D. Pa. 2012) (expert testimony admissible because, inter alia, it is directly relevant to central questions of trial).
  • 31. See Jahn, 233 F.3d at 390 ("In order to be admissible on the issue of causation, an expert's testimony need not eliminate all other possible causes of the injury."). Compare Orthoflex Incorporated v. ThermoTek Incorporated, 986 F. Supp. 2d 776 (N.D. Tex. 2013) (expert failure to rule out alternative causes of product failures did not render his opinions regarding device's defective design unreliable), with Casey v. Geek Squad® Subsidiary Best Buy Stores Limited Partnership, 823 F. Supp. 2d 334, 343–46 (D. Md. 2011) (expert's opinions were unreliable; opinions not based on sufficient facts or data, without any testing; expert failed to rule out alternative hypotheses).
  • 32. Tassi v. Holder, 660 F.3d 710, 721 (4th Cir. 2011) ("[A]n expert is entitled to rely on factual underpinnings—including those based on hearsay—that are 'of a type reasonably relied upon by experts in the particular field in forming opinions or inferences upon the subject.'" (quoting Fed. R. Evid. 703)). See also Strauss v. Credit Lyonnais S.A., 925 F. Supp. 2d 414, 439–40 (E.D.N.Y. 2013) (although expert may rely upon inadmissible hearsay, expert must form own opinions by applying experience and reliable methodology to inadmissible materials; admitting testimony because experts brought to bear expertise and sources used were reasonably relied upon by experts in field). But see Fed. R. Evid. 703 ("Facts or data that are otherwise inadmissible shall not be disclosed to the jury by the proponent of the opinion or inference unless the court determines that their probative value in assisting the jury to evaluate the expert's opinion substantially outweighs their prejudicial effect.").
  • 33. Johnson v. Samsung Electronics America Incorporated, 377 F.R.D. 161, 165–66 (E.D. La. 2011) (admitting testimony, relying in part on Fed. R. Evid. 702 Committee Notes on Rules -- 2000 Amendment).
  • 34. Baldwin Graphic Systems, Incorporated v. Siebert, Incorporated, No. 03 C 7713 (N.D. Ill. Dec. 21, 2005) ("Rule 702 does not prohibit consultation, ban the acquisition of knowledge from other sources, or disqualify any witness who consults with or learns from others.").
  • 35. Fed. R. Evid. 615(3).
  • 36. See, e.g., Malek v. Federal Insurance Company, 994 F.2d 49 (2d Cir. 1993).
  • 37. 4 Weinstein's Federal Evidence § 702.03[1].
  • 38. United States v. Frazier, 387 F.3d 1244, 1262 (11th Cir. 2004) (en banc) (citing 4 Weinstein's Federal Evidence § 702.03[2][a]). For a recent example, see Worley v. State Farm Mutual Automobile Insurance Company, 2013 WL 6478425 (M.D. Fla. Dec. 10, 2013).
  • 39. "Each courtroom comes equipped with a 'legal expert,' called a judge, and it is his or her province alone to instruct the jury on the relevant legal standards." Burkart v. Washington Metropolitan Area Transit Authority, 112 F.3d 1207, 1213 (D.C. Cir. 1997) (reversing Americans with Disabilities Act and Section 504 judgment for deaf plaintff based on erroneous admission of expert testimony respecting requirements governing police encounters with deaf individuals). See also Roundy's Incorporated v. National Labor Relations Board, 674 F.3d 638 (7th Cir. 2012) (affirming exclusion of expert testimony on legalities of property law); Lakeside Feeders Incorporated v. Producers Livestock Marketing Association, 666 F.3d 1099, 1111 (8th cir. 2012) (affirming exclusion of expert testimony as legal conclusion that did not assist trier of fact).
  • 40. Daubert, 504 U.S. at 595. For a recent example of exclusion under Rule 403, see J.T. Colby and Company v. Apple Incorporated, No. 11 Civ. 4060 (S.D.N.Y. May 8, 2013).
  • 41. Fed. R. Civ. P. 26(a)(2)(B).
  • 42. See, e.g., Moore v. International Paint L.L.C., 547 F. App'x 513 (5th Cir. 2013) (excluding expert report, inter alia, because it did not meet Rule 702 standards).
  • 43. Fed. R. Civ. P. 26(a)(2)(B).
  • 44. Daubert, 509 U.S. at 592 n.10.
  • 45. Fed. R. Civ. P. 26(b)(4)(A).
  • 46. Broussard v. Maples, 535 F. App'x 825, 827–28 (11th Cir. 2013) (district court not required to hold hearing). See also Estate of Barabin v. Asten Johnson Incorporated, 740 F.3d 457 (9th Cir. 2014) (hearings are commonly used but not required).