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What Can Expert Witnesses Testify To?


State and federal evidentiary rules and case law limit the types of expert opinions that are admissible in court. Expert testimony is limited to matters of scientific, technical, or otherwise specialized knowledge, about which a jury might not know. Experts can testify about matters covered by their own expertise, so long as their opinions are justified by proper scientific rigor. Read on for a discussion of the types of opinions experts can share, and call a qualified medical expert to ask any additional questions or for help with litigation.

Federal Rule of Evidence 702

FRE 702 governs testimony by expert witnesses in federal cases. Pursuant to FRE 702, qualified experts may testify as to their opinion on a matter governed by their own expertise, provided that:

a. the expert’s scientific, technical, or other specialized knowledge will help the trier of fact understand the evidence or 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.

Experts do not need to rely on personal experience

Lay witnesses cannot testify to matters outside of their own personal knowledge, meaning their own experiences and events that they personally witnessed. Lay witnesses must generally have firsthand knowledge of facts and events to testify. Unlike lay witnesses, experts can form opinions based on various facts of the case as well as their expert knowledge formed by their training, education, and experience.

Experts can testify about reasonableness, causation, and injury

Personal injury matters generally rely on four legal principles: duty, breach, causation, and damages. Experts can offer opinions that touch on any of these elements. For instance, experts may opine on matters of causation and harm. Medical experts, for example, can offer opinions based on a review of the plaintiff’s medical records as well as their educated understanding of the medical field. They could opine, for example, upon whether a certain surgical procedure is known to have common risks and side effects, and further opine on whether, in the specific case, the surgery performed by the defendant likely caused the condition suffered by the patient. They could further opine on the likely severity of the harm and the steps required to mitigate or resolve the issue, touching on damages.

Experts can also testify as to matters of duty and breach. Experts may be qualified to testify as to whether a member of their profession was acting reasonably and in accordance with how one would expect a member of their profession to operate under the given circumstance. For example, a medical expert might offer an opinion as to whether the scientific community accepts a given surgical procedure as a proper treatment for a given ailment, what risks are associated with the treatment (and whether those dangers were adequately disclosed to a patient), and whether a surgery was performed in accordance with proper medical procedure. They might testify that a treatment is still considered experimental or dangerous, or that a defendant erred in their performance so as to cause the plaintiff harm.

Whether their opinion is admissible depends on whether it is helpful to the jury and whether it is adequately supported by scientific rigor.

Practicing Board-Certified Neurosurgeon and Practiced Expert Witness

If you need an experienced, detail-oriented and talented expert witness in a personal injury, medical malpractice, or product liability case, contact the offices of Neurosurgery Medlegal Services, LLC, at 866-659-8051.

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