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Standards for Expert Testimony

Authorities suggest that “lay” witnesses may testify to conclusions drawn from their own observations, while an “expert” expresses an opinion based on special knowledge, skill, experience, training, or education. The testimony of a civil engineer in a 1782 English case may be the first recorded use of expert testimony.

In many lawsuits, the testimony of an “expert” witness is essential for a party to establish their case. Such testimony may be required on numerous issues in a lawsuit, including, for example:

  • How and why the product in a products’ liability case was defective.
  • Whether the actions of the defendant actually caused the injury to the plaintiff, e.g., did exposure to the asbestos really cause the plaintiff’s lung cancer.
  • The standard of care to which a defendant is held in a negligence case, and whether the defendant’s conduct failed to meet this standard.
  • Calculation of damages, e.g., if an injury creates a permanent disability, the amount of award that will compensate for future damages and possible medical procedures and care.

Designating Experts

Experts must usually be qualified by virtue of their education, training, experience, and/or special knowledge. Although procedures vary among states and the federal courts, in most courts, a party planning to call an expert to testify at trial must generally give appropriate notice to all other parties of each expert’s identity and qualifications, and the issues on which the expert will render an opinion. This usually must be done through a formal procedure outlined in applicable state or federal laws and rules of procedure. As a rule, the other parties may then take the expert’s deposition (i.e. out-of-court sworn testimony) and/or hire their own experts to challenge the expert’s conclusions and opinions. Failure, or even delay in designating an expert or providing the required information regarding one’s expert may result in that expert’s testimony not being allowed at trial.

Allowance of Expert Testimony by the Court – The Frye Case

In a 1923 criminal case, Frye v. U.S., the District of Columbia court of appeals considered whether to allow expert testimony regarding the results of a polygraph (lie detector) test. The lower court would not allow the testimony. The court of appeals stated the rule that testimony of experts may be admissible regarding issues where inexperienced persons will not likely be able to form a correct judgment, because it is so related to science, etc., that previous experience or study is necessary. In order to be admissible, however, such testimony must be deduced from a “well-recognized scientific principles or discovery,” that have gained “general acceptance.” The court concluded that polygraph tests had not yet attained that status.

The court admitted that it may be hard to tell exactly when a scientific principle or discovery crosses the line from experimental to well-established. Evaluating the reliability of a test or expert testimony is thus, in a sense, placed upon the scientific community. The Frye test has been used by many courts ever since; if a proposed expert’s testimony is based on “generally accepted” principles, it may be admitted.

The Daubert Case and Admissibility of Expert Testimony

In 1993, the U.S. Supreme Court handed down its decision in Daubert v. Merrell Dow Pharmaceuticals, Inc. which changed the way many courts decide on the admissibility of expert testimony. The heart of the case was whether medication administered to a pregnant mother caused birth defects in her children. The mother offered expert testimony to establish the connection, but the lower court would not allow such testimony, because it felt the testimony did not meet the Frye general acceptance criteria. The U.S. Supreme Court upheld the lower court, but applied different reasoning.

The U.S. Supreme Court rejected the Frye test and stated a new test applicable to the type of scientific evidence at issue in Daubert. The Court stated that inquiry into whether such expert testimony is admissible and reliable must be “flexible,” but focused on the “principles and methodology employed by the expert, not just the conclusions.” Listed factors to be considered included:

  • Whether the theory or technique can and has been tested, and whether there were control standards maintained during the testing, to promote accuracy.
  • Whether it has been subjected to peer review and publication.
  • The statistical potential for errors in the methodology.
  • Whether there is widespread acceptance of it in the relevant scientific community.

These factors were later incorporated into Rule 702 of the Federal Rules of Evidence. In a subsequent case in the 1990’s, the U.S. Supreme Court held that courts should also scrutinize the expert’s reasoning process, as well as methodology. Finally, in 1999 the Court extended the Daubert reliability test to all expert testimony, not just scientific testimony.


It is impossible to generalize about the admissibility of expert testimony in U.S. courts. Federal courts are bound by Daubert and its two related decisions. Since federal rules were involved in Daubert, the decision is not binding on state courts. Some states have adopted the Daubert test, others have adopted it only in part, some states continue to use the Frye test, and another set of states have fashioned their own tests for admissibility.

Especially in states that have accepted Daubert, parties may file a pretrial motion with the court to exclude expert testimony because it does not meet the applicable test for admissibility. Depending on the applicable test, the court may scrutinize the expert’s methodology and reasoning, whether it is widely accepted in the scientific community, and/or other factors. The court will then determine whether the expert will be allowed to testify at trial.

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