Expert witness evidence rules are governed in Federal Court by the 700 series of rules in the Federal Rules of Evidence:
Rule 702. Testimony by Expert Witnesses
A witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwise if:
(a) the expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue;
(b) the testimony is based on sufficient facts or data;
(c) the testimony is the product of reliable principles and methods; and
(d) the expert has reliably applied the principles and methods to the facts of the case.
Author’s Note: Rule 702 is unquestionably the most important of the expert evidence rules as it covers both the requirement for qualifying the expert witness as well as requirements for the expert’s methodology. Rule 702 can serve as an excellent checklist for both direct and cross examination of expert witnesses.
Rule 703. Bases of an Expert’s Opinion Testimony
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. But if the facts or data would otherwise be inadmissible, the proponent of the opinion may disclose them to the jury only if their probative value in helping the jury evaluate the opinion substantially outweighs their prejudicial effect.
Author’s Note: Rule 703 allows expert witnesses to rely on hearsay in many circumstances. For example, a civil engineer may be able to rely upon a report from a geotechnical expert witness or a surgeon may be able to rely upon the report of a radiologist.
Rule 704. Opinion on an Ultimate Issue
(a) In General — Not Automatically Objectionable. An opinion is not objectionable just because it embraces an ultimate issue.
(b) Exception. In a criminal case, an expert witness must not state an opinion about whether the defendant did or did not have a mental state or condition that constitutes an element of the crime charged or of a defense. Those matters are for the trier of fact alone.
Author’s Note: Rule 704 was enacted as part of the backlash against the insanity defense following John Hinkley being found not guilty by reason of insanity of the attempted assassination of President Ronald Reagan.
Rule 705. Disclosing the Facts or Data Underlying an Expert’s Opinion
Unless the court orders otherwise, an expert may state an opinion — and give the reasons for it — without first testifying to the underlying facts or data. But the expert may be required to disclose those facts or data on cross-examination.
Author’s Note: Rule 705 allows expert evidence to be presented more succinctly during direct examination.
Rule 706. Court-Appointed Expert Witnesses
(a) Appointment Process. On a party’s motion or on its own, the court may order the parties to show cause why expert witnesses should not be appointed and may ask the parties to submit nominations. The court may appoint any expert that the parties agree on and any of its own choosing. But the court may only appoint someone who consents to act.
(b) Expert’s Role. The court must inform the expert of the expert’s duties. The court may do so in writing and have a copy filed with the clerk or may do so orally at a conference in which the parties have an opportunity to participate. The expert:
(1) must advise the parties of any findings the expert makes;
(2) may be deposed by any party;
(3) may be called to testify by the court or any party; and
(4) may be cross-examined by any party, including the party that called the expert.
(c) Compensation. The expert is entitled to a reasonable compensation, as set by the court. The compensation is payable as follows:
(1) in a criminal case or in a civil case involving just compensation under the Fifth Amendment, from any funds that are provided by law; and
(2) in any other civil case, by the parties in the proportion and at the time that the court directs — and the compensation is then charged like other costs.
(d) Disclosing the Appointment to the Jury. The court may authorize disclosure to the jury that the court appointed the expert.
(e) Parties’ Choice of Their Own Experts. This rule does not limit a party in calling its own experts.
Author’s Note: Rule 706 remains sparsely used in most civil cases. The overwhelming majority of expert witnesses in civil cases are selected and compensated by a litigant in the case.