To understand the law relating to expert witnesses, one must first understand the law relating to witnesses generally and the special treatment afforded those with special expertise. For most witnesses, courts want the same thing that Joe Friday wanted on the "Dragnet" television series: "Just the facts, Ma'am!" Fearing that any departure from precise factual observations would usurp the jury's role in evaluating the evidence, courts have traditionally prohibited lay witnesses from offering their opinions on the evidence or departing, even to the slightest degree, from a purely factual recitation of events which the witness personally observed. Throughout most of American legal history, ordinary citizens who dared to take the witness stand needed three things -- the capacity to observe, to remember and to relate.
Like most evidentiary rules, courts have relaxed this restriction considerably over the years. Under Rule 701 of the Federal Rules of Evidence, lay witnesses may testify in the form of opinions or inferences which are "(a) rationally based on the perception of the witness and (b) helpful to a clear understanding of the witness' testimony or the determination of a fact in issue." Accordingly, there are two types of opinions which laypersons are permitted to convey from the witness stand: First, laypersons may testify in the form of what has been described as "lay shorthand" where it would be impossible to communicate the facts without departing from strict factual language. Thus, while Mr. Spock of Star Trek fame would testify that "an excess of moisture was emanating from her tear ducts," a lay witness may depart from such uncompromising precision by testifying simply that "she was crying." Such testimony, while involving an opinion inferred from factual observations, is essential to a clear understanding of the witness' testimony.
Second, lay witnesses may convey the type of opinion which normal persons form constantly and correctly. Thus, a layperson may state that she heard a "siren" even though the identification of such a noise truly amounts to an opinion based upon the sound observed. Lay witnesses have also been permitted to testify regarding such emotional states as anger or upset, speeds of vehicles, whether someone appeared to be in pain, behaved in a drunken manner, had an honest reputation, or to similar opinions within the common experience of common persons and rationally based upon their perceptions.
Although the Federal Rules of Evidence have replaced a strict exclusion of lay opinions with the relaxed requirement that lay opinions must ultimately be "helpful" to the trial process, courts exercise considerable discretion in limiting lay testimony to elicit more precise factual accounts. At bottom, while some small amount of opinion testimony is reluctantly tolerated as a necessity of communication, ordinary persons taking the witness stand must still "stick to the facts" when testifying.
Expert witnesses are far from ordinary. Although the rest of us are limited largely to our personal observations, those who qualify as "experts" shed the limitations of mortal witnesses and are endowed with the power to render opinions and to provide other information far exceeding personal observations. If exercised properly, this power may be harnessed to present powerful testimony at trial and, ultimately, a powerful and winning case. To do so, the advocate must know when to use expert testimony, how to qualify an individual as an expert whose views will carry weight with the jury, and how to use the expert to lend an air of credibility and strength to the case as a whole.
A. When Is Expert Testimony Permitted?
Although expert testimony has traditionally been used in medical malpractice cases, and many attorneys fail to recognize their value in other contexts, expert testimony is permitted -- and quite effective -- in many types of cases. Under Rule 702 of the Federal Rules of Evidence, expert testimony is permitted whenever it would be helpful to the factfinder in understanding the case:
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.
Before a court will admit expert testimony, it must be satisfied that (1) the witness qualifies as an expert; (2) the field of expertise and underlying methodology is sufficiently reliable and valid to place before the jury; and (3) such testimony will truly assist the jury in understanding the case or in determining material issues.
1. Qualifying the Expert
Despite the stereotype, the Federal Rules of Evidence do not require that one obtain an "M.D." degree before taking the witness stand as an expert. Unlike most employers seeking to fill important jobs, federal judges do not require a degree as a prerequisite for expert testimony. Instead, the expert must possess knowledge, education or experience beyond that of the ordinary juror which will enable that person to assist in the trial process. While formal education may be helpful and even essential in some areas, expertise may be acquired far from the classroom in a variety of fields. Thus, where the plaintiff wishes to prove that her one hundred pound dining room table was damaged when the defendant's moving van improperly drove over a speed bump at thirty miles per hour, her best expert may be a truck driver who, after quitting high school, has spent a lengthy career transporting similar furniture in trucks of similar size. If the court is satisfied that this person has expertise not possessed by ordinary laypersons which will help the jury in understanding how the furniture may have shifted, that person may qualify as an expert despite the lack of a degree in physics.
Before eliciting an expert's opinion, one must take great care in establishing the witness' qualifications to the court's -- and the jury's -- satisfaction. In determining whether the witness possesses sufficient expertise, the court will evaluate the person's education, experience and knowledge in comparison with laypersons -- not other experts. Thus, a family doctor may testify as an expert on a specialty within medicine such as orthopedics despite the availability of orthopedic surgeons who possess even greater expertise.
While courts do not require that parties proffer the foremost expert in a particular field, effective advocates must elicit their qualifications from the witness stand in such a manner that jurors will trust and rely on their opinions. On direct examination, the attorney proffering the expert must present the jury with an "oral resume" of the witness, delving into her extensive education, training, knowledge and experience. Although opposing counsel may offer to stipulate to the witness' expertise in an effort to curtail the parade of credentials, smart advocates must march on with these qualifications in order to impress the jury with the witness' credibility.
Despite the importance of credentials, trust and credibility require more than a fancy resume. Indeed, the expert who is offered to the jury as a "know-it-all" may subliminally challenge jurors to contest the expertise of an egotistical or pompous witness. When conveying credentials, the attorney and the witness must be careful to show the witness' human side, thereby fostering an essential rapport between the expert and the jury. Beyond anything written on a resume, eye contact with jurors, clear communication and even some measure of modesty in the presentation of impressive achievements may be the most important credentials of all.
By the time that an advocate formally offers the witness as an expert in a particular field, earlier testimony should enable the attorney to do so proudly with little doubt as to the court's and the jury's acceptance of these qualifications.
2. The Field of Expertise
Expert astrologers do not get to testify. Although Madam Isabella may possess astrological knowledge, skill, experience and training far in excess of ordinary laypersons, these clairvoyant powers will not overcome the exclusionary power of a federal judge.
Before admitting expert testimony, federal judges must screen the underlying methodology to ensure that it is both reliable and valid. Recognizing the unique aura of credibility with which jurors often regard expert testimony, particularly scientific testimony and evidence, courts have traditionally placed great limits on the areas in which experts may testify. Under the longstanding test of Frye v. United States, 293 F. 1013 (D.C. Cir. 1923), "while the 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 to which it belongs."
While this Frye test served as the principle basis for excluding many areas of potential expert testimony for seventy years, the United States Supreme Court replaced this test in the landmark case of Daubert v. Merrell Dow Pharmaceuticals, Inc., 113 S. Ct. 2786 (1993). Concluding that the Frye test was "incompatible with the Federal Rules of Evidence [and] should not be applied in federal trials," the Supreme Court rejected Frye's general acceptance test in favor of a more "liberal" approach to the admissibility of scientific evidence. The Daubert Court held that trial judges must carefully screen "scientific" evidence to ensure that it is both reliable and valid. In so doing, trial judges must determine whether the expert is proposing to testify to (1) scientific knowledge that (2) will assist the factfinder in understanding the issues presented. "This entails a preliminary assessment of whether that reasoning or methodology properly can be applied to the facts in issue." Id.
Expressing confidence that "federal judges possess the capacity to undertake this review," the Court declined to establish a precise test for the reliability and validity of such evidence. Instead, the Court made some "general observations" about the reliability and validity of scientific evidence, suggesting that trial judges consider, inter alia, the following four factors:
1. Is the theory or technique at issue testable, and has it been tested?
2. Has the theory or technique been subjected to peer review and publication? While publication is not required, "submission to the scrutiny of the scientific community is a component of 'good science,' in part because it increases the likelihood that substantive flaws in methodology will be detected."
3. In the case of scientific techniques, what is the known or potential error rate? Are there standards controlling the operation of the technique?
4. Is the theory or technique generally accepted in the scientific community? While no longer a prerequisite to admissibility, general acceptance "can be an important factor in ruling particular evidence admissible." By contrast, techniques which are known but not widely accepted "may properly be viewed with skepticism."
Although the Daubert factors give federal judges considerably more discretion in determining appropriate areas of expert testimony, it is unlikely that Madame Isabella and her astrological colleagues will ever pass this test and assume the coveted role of expert witness. Nonetheless, the Supreme Court's departure from a "general acceptance" test will likely increase the areas in which expert witnesses may testify.
While many appellate decisions focus on the dangers presented by novel scientific testimony, expert testimony need not be rooted in science. As Rule 702 reminds us, experts may also testify on the basis of "technical, or other specialized knowledge" so long as the realm of expertise is sufficiently reliable and relevant to assist the factfinder in understanding the case.
3. Helpfulness of Expert Testimony
Under common law, experts were only permitted to take the stand if the subject matter of their testimony was arcane or beyond the common understanding of jurors. Rejecting this requirement, Rule 702 merely requires that such testimony "assist the trier of fact to understand the evidence or to determine a fact in issue." See Kopf v. Skyran, 993 F.2d 374, 377 (4th Cir. 1993). In short, expert testimony must be "helpful."
Applying this rule, courts should exclude the testimony of experts who are no more capable than the jury of drawing certain inferences or conclusions. While an orthopedic surgeon's testimony is essential in determining the presence of post-traumatic lumbar instability, the same expert may not be helpful where common sense and logic will suffice. Thus, the same orthopedic surgeon may be precluded from taking the stand on behalf of a plaintiff amputee to testify that "removing the wrong leg is contrary to accepted medical practice." Where laypersons can easily draw the necessary conclusions, courts should not permit experts to intrude upon or even insult the intelligence of the jury by proffering un-enlightening and time-consuming testimony.
B. Challenging Experts on Voir Dire
Assuming that the party proffering the expert has done so with care, the opponent will rarely succeed in excluding expert testimony by attacking qualifications on voir dire. However, in certain situations, limited and strategic cross-examination at this early stage may help to limit the witness' range of expertise and undermine an appearance of invincibility even before the expert has testified to the substance of the case. Even the most qualified of experts may lack some credentials or experience of importance in analyzing the case at hand.
Ultimately, the decision whether to pursue gaps in expertise on voir dire or to save such questions for later cross-examination is one of strategy. Many advocates believe that questions regarding the extent of one's expertise (as opposed to whether a witness should qualify as an expert in the first place) should always be reserved for the impeachment phase of cross-examination. These attorneys emphasize that voir dire is only designed for questions bearing on the court's preliminary determination of competence to testify. By contrast, other attorneys claim that, in certain situations, the opportunity to take an early aim at an expert's credentials will help to awaken the jury's sense of skepticism during the witness' substantive testimony.
While this opportunity should not be waived without deliberation, many attorneys misuse voir dire in strategically misguided ways. When confronted with a board-certified neurosurgeon and author of a multi-volume treatise on cerebral concussions, questions aimed at an expert's credentials may often be answered in ways which enhance the witness' credibility. Even where some gaps in qualifications do exist, the jury may well dismiss these inadequacies in light of a subsequent judicial ruling that the individual is nonetheless qualified as an expert in the field. Indeed, the court's ruling in favor of the witness' expertise may be viewed as a rejection of any attempt to contest the witness' credibility. If so, an early attack on voir dire may unwittingly enhance the witness' persuasive power rather than undermine it.
If counsel nonetheless decides to pursue questions on voir dire, questioning should not involve such impeachment issues as bias or lack of familiarity with certain material facts of the case. These issues are more appropriately raised on cross-examination since they do not relate to the witness' competence to testify in the first place. Thus, in many cases, the best approach to voir dire consists of "No questions, your Honor."
C. Limitations on Expert Testimony
Once qualified, experts have few restrictions on the manner in which they may testify. As the Federal Rules of Evidence indicate, experts "may testify ... in the form of an opinion or otherwise." Fed. R. Evid. 702. Indeed, experts may share their specialized knowledge by explaining relevant principles without formulating a precise opinion. As long as the testimony is helpful, it is generally admissible.
Yet, in some circumstances, we fear that expert testimony may be too helpful. This is particularly true where experts testify to the ultimate issue in the case. Although courts have traditionally excluded such testimony as usurping the role of the factfinder, the Federal Rules of Evidence reversed this exclusionary trend. According to Rule 704(a), "testimony in the form of an opinion or inference otherwise admissible is not objectionable because it embraces an ultimate issue to be decided by the trier of fact."
Though the Federal Rules remove certain restrictions on expert testimony, they do not remove all barriers. "The promulgation of Rule 704 does not mean that witnesses will now be able to give testimony that involves nothing more than choosing up sides." Waltz, The New Federal Rules of Evidence 112 (2d ed. 1974). Ultimately, the trial court has considerable discretion in excluding opinions which underlie or unnecessarily invade the province of the jury or otherwise exceed the proper bounds of expert testimony. While these discretionary calls have produced little uniformity in the law, courts are particularly sensitive where experts testify like lawyers rather than technical specialists. Thus, courts often exclude testimony phrased in terms of inadequately explained legal criteria or legal jargon. This is particularly true where the expert failed to convey her testing in the form of specific facts, testified in a conclusory manner, or gave the appearance of instructing the jury on the law by deliberately testifying in terms of the applicable legal standard. See United States v. Scap, 846 F.2d 135, 140-42 (2d Cir. 1988), on rehearing, 856 F.2d 5 (2d Cir. 1988). Indeed, counsel must vehemently object where experts testify to mixed questions of law and fact involving considerations beyond the scope of their expertise. In many cases, rather than excluding such testimony, courts will simply instruct the jury that it is not bound by the expert's opinion and is free to draw its own conclusion.
Although opinions on the ultimate issue are tolerated in many cases, they are expressly forbidden in certain criminal cases. In the wake of John Hinckley's acquittal by reason of insanity in the shooting of President Ronald Reagan, Congress has prohibited experts from testifying to whether an accused possessed a mental condition constituting an element of, or defense to, the crime charged.
No expert witness testifying with respect to the mental state or condition of a defendant in a criminal case may state an opinion or inference as to whether the defendant did or did not have the mental state or condition constituting an element of the crime charged or of a defense thereto. Such ultimate issues are matters for the trier of fact alone.
Fed. R. Evid. 704(b).
D. Bases of Expert Testimony
Unlike other witnesses, experts are not limited to their personal observations when testifying. In fact, experts may be very helpful even where they have no personal observations at all. According to the Federal Rules of Evidence, experts may base their testimony on a variety of sources -- even information which would not itself be admissible in evidence:
The facts or data in the particular case upon which an expert bases an opinion or inference may be those perceived by or made known to the expert at or before the hearing. If of a type reasonably relied upon by experts in the particular field in forming opinions or inferences upon the subject, the facts or data need not be admissible in evidence.
Fed. R. Evid. 703
Thus, an expert may use the following sources of information when taking the witness stand:
1. Personal Knowledge
Experts who played an actual role in the facts underlying the case, such as treating physicians, may base their opinions on their own observations. Because experts are often impeached for lack of personal knowledge, the advocate should make some effort, if feasible, to provide the expert an opportunity to obtain personal observations of certain facts. For example, while a physician testifying for the defense in a personal injury case may dispute the plaintiff's injury on the basis of cold medical records, arranging for an examination of this patient may lend greater credibility to this opinion -- particularly where the plaintiff's experts consist of treating physicians who may testify from first hand observations of the patient's condition. This may even be true where such an independent medical examination would add little, if any, additional information.
2. Evidence Admitted at Trial
An expert may listen to testimony or review documents admitted at trial as a means of informing his opinion. Furthermore, the facts relevant to the expert's opinion may be conveyed to the expert on the witness stand in the form of a hypothetical question so long as these facts are ultimately admitted into evidence. Fluckey v. Chicago Northwestern Transp. Co., 838 F.2d 302 (8th Cir. 1988).
3. Evidence or Information Conveyed Before Trial
Typically, the expert will review evidence or other information long before taking the stand. While such data need not be disclosed by the expert before giving her opinion, it is fully discoverable and may be pursued on cross-examination. See Fed. R. Evid. 705.
4. Reliance on Other Experts' Opinions
In rendering an opinion on the witness stand, experts may rely upon other experts' opinions so long as they are of the type reasonably relied upon by experts in the particular field in forming opinions or inferences upon the subject. Fed. R. Evid. 703. For example, a medical examiner may rely upon a pathologist's classification of blood type when testifying to the cause of death. This permits parties to streamline the presentation of cases by calling a single expert rather than a number of individuals testifying to subsidiary opinions. However, the expert may not rely upon another's opinion on the very same issue to which the expert is testifying. Thus, the same medical examiner may not rely upon another expert's opinion regarding the cause of death.
5. Inadmissible Sources
Strange as it may sound, experts may base their opinions on information which the jury may not consider in reaching a verdict. As long as the information is "of a type reasonably relied upon by experts" in rendering such opinions, even inadmissible hearsay may provide the basis for an expert's opinion. Indeed, much of the information used by experts consists of hearsay gleaned from the expert's formal education, review of pertinent literature, or during one's practice.
Because experts are permitted to rely upon inadmissible information in certain circumstances, attorneys have been known to take advantage of this rule by calling expert witnesses to serve as conduits through which hearsay is brought before the jury. Although experts are frequently allowed to disclose otherwise inadmissible hearsay and other evidence for the limited purpose of justifying their opinions, such information is not admissible for its truth.
To prevent undue prejudice from the disclosure of otherwise inadmissible information, the court may instruct the jury as to the limited purpose for which such information is conveyed. Engebretsen v. Fairchild Aircraft Corp., 21 F. 3d 721, 729 (6th Cir. 1994). However, such limiting instructions may not be very effective in curbing the jury's misuse of such information. Therefore, when a court suspects that the expert is either serving as a conduit for the dissemination of inadmissible hearsay, or where conveying such information poses a substantial risk of unfair prejudice, the court should exercise its discretion to preclude disclosure of such information. Pelster v. Ray, 987 F. 2d 514, 525-27 (8th Cir. 1993). Furthermore, where there are constitutional or policy-based statutory prohibitions rendering certain information inadmissible, experts may be precluded from using such information in support of their opinions despite the language of Rule 703. See Estelle v. Smith, 451 U.S. 454 (1981); Robertson v. Union Pacific R.R. Co., 954 F.2d 1433, 1435 (8th Cir. 1992).
While it would not be proper for trial counsel to disregard restrictions on the use of inadmissible hearsay and other evidence, effective advocates must recognize the strategic advantages of placing such information before the jury in the context of expert testimony. Where such information is disclosed for the legitimate purpose of supporting the expert's opinions, trial attorneys may succeed in presenting indirectly the type of information which they could never admit independently. When planning trial strategy, this fringe benefit of expert testimony must be considered.
E. Disclosing Grounds for Expert Opinion
Contrary to common law, Rule 705 of the Federal Rules of Evidence abandoned the requirement that experts disclose the facts upon which they based their opinions prior to conveying them:
The expert may testify in terms of opinion or inference and give reasons therefor without first testifying to the underlying facts or data, unless the court requires otherwise. The expert may in any event be required to disclose the underlying facts or data on cross-examination.
Fed. R. Evid. 705. While the expert could theoretically provide his qualifications and only testify to his ultimate conclusions in a case, such testimony would hardly be effective in persuading the factfinder to accept these unsupported opinions. To the extent that the expert fails to disclose the bases for such opinions on direct examination, the underlying facts or data must be disclosed if such information is pursued on cross-examination. Of course, Rule 705 also permits the court to require that the expert disclose the bases for her opinions before providing them. Yet, because Rule 705 is designed to streamline the presentation of expert testimony, courts rarely interfere with such presentations in this manner.