Expert Testimony

The Importance of Expert Witnesses

Learning the elements of a personal injury claim is vital to understanding how expert witnesses can strengthen a personal injury claim. Because the burden of proof is on the plaintiff to prove each element of a negligence case, an expert witness may be necessary to bolster an argument that a defendant had a duty of care to the plaintiff, breached that duty, caused the plaintiff’s injuries, or that the plaintiff suffered certain damages.

Depending on state rules, expert witnesses may testify at trial if scientific, technical or other specialized knowledge will assist the jury or judge in understanding the evidence or deciding a fact at issue in the case. A witness is qualified as an expert based on their knowledge, skill, experience, training, or education. An expert witness may be permitted to testify at trial if their testimony is based on sufficient facts or data, is the product of reliable principles and methods, and they have applied the principles and methods reliably to the facts of the case.

This rule is meant to ensure that experts presented in court (in both civil and criminal cases) are legitimate and that they present their opinions based on sound reasoning. In other words, if a proposed expert witness is a conspiracy theorist whose testimony lacks any sort of evidentiary basis, then they will not be permitted to testify. This is important, because expert witnesses should add clarity to the case and help the judge or jury determine the truth of what actually happened — and whether the defendant should be held responsible.

There are a number of different types of experts that may be used in a personal injury case. Some experts consult with attorneys to help explain important issues, while others testify at trial. In any given personal injury case, the following expert witnesses may be utilized:

  • Medical experts: to testify or consult about the victim’s injury, their treatment, and prognosis
    • Mental health experts: to testify or consult about how the injury has impacted the victim’s mental and emotional state
    • Accident reconstruction experts: to testify or consult about how the accident happened using drawings, models and computer programs
    • Engineering experts: to testify or consult about the construction of a building or roadway and how it may have contributed to an accident
    • Manufacturing experts: to testify or consult about how a product was defective or improperly designed
    • Economics or financial experts: to testify or consult about how the injury has affected the victim’s financial status (lost earning capacity, etc.)

These expert witnesses can provide vital information at any stage of a trial — or before trial — that will support a plaintiff’s case.

While expert witnesses are often costly to hire, they can provide crucial information and testimony. Depending on the facts of the case, an expert witness may even allow your attorney to negotiate a favorable settlement rather than having to take the case to trial. If your case does go to trial, having one or more expert witnesses may be essential to a successful outcome. 

Federal Rule:

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.

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.

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.

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.