One of the nuances of litigation that can be confusing to expert witnesses is when their expert testimony is heard away from the jury. In some cases, a whole day’s worth of testimony is heard ‘behind closed doors.’ This confuses expert witnesses; they are subject matter experts in their line of work, often with years of education and experience in their particular discipline. Why isn’t the jury able to hear the expert’s facts and findings after hours of preparation for the case? Isn’t the expert witness’s testimony…good enough?
Our Federal Rules of Evidence require expert testimony to be validated before a jury can hear it. If an expert witness relies on information to form an opinion that is otherwise inadmissible to the court, then the court needs to ensure the inadmissible information remains where it belongs: out of the court. Inadmissible underlying information is not admissible simply because the expert witness’s opinion or inference is accepted in the eyes of the court. The court (and parties) have the opportunity to hear the expert witness testimony to ensure it meets the rules.
Rule 703 (Bases of an Expert) of the Federal Rules of Evidence states:
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.
At the risk of prejudice, a jury can potentially misuse information once heard at trial; no one can ‘unhear’ testimony, so the court needs to ensure the expert witness’s testimony is admissible before it is presented to the jury. A simple analogy is the toothpaste analogy: once it’s out of the tube, it’s awfully hard to get toothpaste back in its packaging. Expert witnesses should bear in mind the Rules of Evidence and be prepared for this procedural norm in litigation.