expert witness

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An expert witness is a person with specialized knowledge, skills, education, or experience in a particular field who is called upon to provide their expertise in legal proceedings to assist the court with understanding complex technical or scientific issues. See Finding and Researching Experts and Their Testimony White Paper. Each party selects their own expert witness, and those experts are usually paid a fee for their consultation and their testimony. Experts may be located in a variety of ways, including prior lawsuits, and online resources such as the JurisPro Expert Witness Directory.  

A person who is designated as an expert witness must be qualified on the subject of their testimony. See Federal Rule of Evidence 702. The court serves as a “gatekeeper” to screen out experts who are unqualified, their expertise is irrelevant to the facts at issue, or their methods are unreliable.  Usually, the court will determine the admissibility of an expert witness’ testimony in a pre-trial hearing.

The U.S. Supreme Court established the standard for expert testimony admissibility in Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993). In this case, the Court established guidelines for determining the admissibility of expert witness testimony. These factors to be considered are: 

  1. Whether the technique or theory in question can be and has been tested; 
  2. Whether it has been subjected to publication and peer review; 
  3. Its known or potential error rate; 
  4. The existence and maintenance of standards controlling its operation; and 
  5. Whether it has attracted widespread acceptance within a relevant scientific community.  

This is known as the Daubert Standard. Most state courts follow this gatekeeping standard. These criteria intend to prevent unreliable or otherwise “junk science” from being heard as evidence in an expert’s substantive testimony. The burden is on the proponent of the testimony to establish its admissibility by a preponderance of proof. It is possible that an otherwise admissible expert witness might offer a novel theory that itself could be subject for exclusion. An expert would have to be prepared to present the science behind the theory to be able provide an opinion on that subject. The standards for admissibility may vary from one jurisdiction to the next. Therefore, admissibility of controversial or emerging theories may change from one court to the next.  

Generally speaking, those who qualify as experts may testify about their conclusions so long as their analysis is scientifically sound, is helpful without usurping the role of the judge or jury, and is based on their background and experience. Unlike lay witnesses, expert witnesses may provide opinions on evidence such as the genuineness of documents, accident reconstruction, and computer forensics.  In reaching their conclusions, experts may perform independent examinations of a party, make site visits, and review evidence in forming their opinion.  

In federal court, experts must prepare a report summarizing their analysis and conclusions, and share the report with all other parties. See: disclosure, expert witness disclosure, and Rule 26(a) of the Federal Rules of Civil Procedure. This allows other parties to effectively cross-examine the expert.

Experts may be designated by a party as “testifying” or “non-testifying.” The distinction lies in their roles and the extent to which they participate in a legal case. While testifying experts provide testimony during trial, the non-testifying expert primarily works in an advisory capacity, offering consultation and support during pre-trial preparations.  

[Last updated in August 2023 by Jim Robinson, Esq., JurisPro Expert Witness Directory]