Federal Rule 703: Basis of Expert Witness Opinion

Federal Rule of Evidence 703 establishes the basis on which experts may form their opinions. Such opinions are needed for a jury to understand the facts in a case and the evidence before them. Generally, such expert testimony is necessary to prevail in trial matters.

Attorney meeting with an expert witness

ByEdward Maggio, J.D., M.S.


Updated on June 18, 2024

Attorney meeting with an expert witness

While establishing guidelines for what can be admitted at trial, Rule 703 does create an opportunity for using inadmissible evidence. In particular, this opportunity has been the subject of both praise and scrutiny over the years. Federal rules of evidence dictate the parameters under which such evidence may be considered. Inadmissible evidence can be heard by a jury under certain key circumstances.

What is FRE 703?

Federal Rule of Evidence 703 specifically states that:

“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.”

In summary, evidence from experts can be based on a few sources. The first is the witness’s own interpretation of evidence viewed by them with generally accepted opinions based on it. The second source involves discussion by an expert on the current practices in their chosen field.

Inadmissible Evidence

In compliance with the rule itself, experts can base their opinions on inadmissible evidence as long as such proof is fair to rely on. Moreover, the inadmissible evidence can only be disclosed to the jury within the limits of any prejudice to the other side. Even as inadmissible evidence, a skilled trial attorney can still develop a plan to create an opportunity to influence a jury. Such opportunities are often very nuanced as a legal approach.

For example, a doctor admitted to testify may be excluded from discussing the causes of industrial poisoning in children. The reason being is this expert is not a chemical expert nor has any clinical experience with industrial poisoning. However, the doctor can end up testifying about their training and experience with poisoned children. By discussing their experience, they indirectly leave the jury with a view on causation. Such a view would prejudice the defendant in an industrial poisoning case. To curb such perceived abuses, courts may invoke a number of safeguards to prevent litigants from using FRE Rule 703 as a loophole.

Alternative Solutions

Some federal courts take a very restrictive approach when it comes to inadmissible evidence. They may require the expert to classify the information used for their judgment in only general terms. The court may also require the attorney to classify the evidence in advance of trial. In addition, under this approach, courts often prohibit the expert from reading or explaining the information to the jury members from any inadmissible source. This essentially puts a complete ban on even discussing the work product of other experts if deemed inadmissible.

However, a majority of jurisdictions prefer a broader scope and to address the situation on a case-by-case basis. They often allow the underlying factual information to be permissible for a limited purpose. That purpose is the basis for justifying the opinion of the expert. However, the information is not treated as substantive evidence. In turn, a jury will be given a restrictive explanation on how they should use or view such information.

An advantage of the majority approach is that it gives the jury all the facts. It shares all the detailed information an expert relied upon in forming their opinion, allowing the jury to make a decision as to the validity of the expert’s conclusions. Using this approach reduces the temptation to use Rule 703 as a back door exception to the hearsay rule.

About the author

Edward Maggio, J.D., M.S.

Edward Maggio, J.D., M.S.

Dr. Edward Maggio, Esq. is a respected lawyer and academic, known for his contributions to criminal justice and legal education in New York. He holds a Doctorate in Law from New York Law School, a Master of Science in Criminology from Oxford University, and a PhD in Religion from the University of Sedona. As an Assistant Professor at the New York Institute of Technology and an adjunct professor at Dowling College, Dr. Maggio has shared his extensive knowledge in human behavior, human rights, and societal relationships. In 2012, he founded his own law practice, focusing on a variety of legal and security needs. Dr. Maggio is also a seasoned conference organizer, author of books on private security and white-collar crime, and a consultant for law enforcement and business professionals. His career is marked by a continuous pursuit of knowledge and a commitment to educating others in the fields of criminal justice and security.

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