What Is an Expert Witness?
Written by: Michael Talve
Expert witnesses are those with specialized skill sets whose particular opinion may be helpful to the jury when the factual evidences of the case are not enough. Testimonies from expert witnesses can have tremendous influence on the final decision of the judge. Hence, the admissibility standards of experts are strictly outlined in the Federal Rule of Evidence (FRE) 702, with specific definitions of (a) the qualifications of the expert witnesses and (b) the level of admissible testimony. Only when the expert meets these requirements will he or she satisfy the standards of a reliable expert witness.
Federal Rule of Evidence 702
The requirements defined in the FRE 702 can be divided into four main pillars:
We have attempted to briefly summarize these four pillars in this post:
Admissibility of an Expert Witness
An expert witness must:
- be skilled in his/her particular profession (relevant to the issue of the case)
- have specialized knowledge through training, education, or practical experience
The expert is qualified to opine on the case if and only if his or her professional knowledge and skill set will assist the jury better understand the evidence. The knowledge of the expert must be above and beyond the knowledge of the jury. He or she does not necessarily have to be the best in the field, nor be equipped with all of the facts regarding the case as long as his or her expertise is relevant.
Admissibility of the Expert’s Testimony
The testimony by the expert must be based on:
- sufficient data and factual information
- accepted principle and methods that are in common use in the field
- appropriate application of the principles and methods
The expert’s testimony is admissible as long as the expert uses unambiguous data and follows the standard of practice in his or her field of expertise.
An expert must be able to add value to the case by assisting the fact finder. Therefore, the expert testimony must:
- provide reliable opinion to help the fact finders reach a conclusion
- include valid scientific connections of the evidences of the case that were not previously apparent
An expert is not considered helpful if his or her assumptions do not apply to the facts of the case. The expert must make sure that there is no analytical gap in his or her reasoning, and must provide information that is new and not obvious to the jury.
The opinion of the expert must be based on foundational facts. Such facts are agreed upon by other experts in the same field. Thus, these facts from which the expert derives his conclusion must be accurate and pertinent to the issue of the case.