What is the Definition of an Expert Witness?

The Legal Requirements to Qualify As an Expert Witness

Federal Rule of Evidence 702 governs the qualifications of expert witnesses.

Fed. R. Evid. 702. Expert Witness Testimony

Expert Witness Definition
If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, an expert witness is qualified by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise, if (1) the testimony is sufficiently based upon reliable 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.

The role of an expert witness is to use “scientific, technical, or other specialized knowledge” to assist the trier of fact to “understand the evidence or to determine a fact in issue.”  The “trier of fact” is the jury in a jury trial and the judge in a bench trial (a trial without a jury).  The rationale for Rule 702 is that the jury may not be able to understand or correctly decide a case without assistance from experts.

Experts are qualified to testify by their “knowledge, skill, experience, training, or education.”  Note the conjunction “or.”  Under Rule 702, the expert only needs to have “knowledge,” “skill,” “experience,” “training,” or “education.”  She need not have all five.

Expert witnesses will routinely be qualified at the beginning of direct examination by the counsel who has retained them.  The expert can expect to be asked about her:

  • profession,
  • education,
  • training,
  • employment,
  • experience,
  • certifications/licenses,
  • specialties,
  • present title,
  • practical experience,
  • number of examinations/investigations performed,
  • lecturing or teaching,
  • research work,
  • awards,
  • published works,
  • memberships in professional associations, and
  • when and where she previously qualified to testify as an expert.

Some expert witnesses may feel uncomfortable going over their credentials and professional accomplishments in open court.  The extent of the “qualifying” testimony should be reviewed with counsel during pre-trial preparation.  It is the responsibility of counsel to decide how much of the background, experience, and expertise of the expert to put before the jury.  Counsel should attempt to impress the judge and jury without putting them to sleep.

Under Rule 702, it is the judge who initially determines if an expert’s proposed testimony, as a matter of law, will satisfy the Rule’s requirements.  If an expert’s qualifications are challenged, the judge may have him voir dired.  This means that the expert will provide preliminary testimony on his qualifications via direct and cross-examination.  Based on the testimony he provides during the voir dire, the judge will then make her ruling on whether the expert witness is qualified to testify.

If the judge holds that the expert is not qualified to testify on a particular area, then the expert will not be allowed to testify on that area.  The judge’s decision in this regard is an issue that may be raised on appeal, but the standard of review is usually whether the trial judge abused her discretion in holding that the expert was not qualified.  This is a difficult standard to meet.

If the judge finds that the expert witness is qualified, he will be allowed to state his opinion only in the areas in which he was qualified, not on any and all matters or issues.[1]  Qualified experts are allowed to testify by expressing an opinion.  This is in stark contrast to lay witnesses, who can usually only testify to firsthand personal knowledge.  The issue of an expert’s qualifications will be determined on a case by case basis.

The facts of a particular case will dictate the expertise needed by the proffered witness.  The fact that a witness may have qualified previously in a particular case does not necessarily mean he will be found qualified in subsequent cases.

[1] Of course, the expert’s proposed testimony could still be challenged under the Daubert line of cases.

Excerpted from the SEAK text; How to be a Successful Expert Witness