What Is an Expert Witness?


What Is an Expert WitnessExpert 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. Due to those skills, testimonies from expert witnesses can have tremendous influence on the final decision of the judge. As such, 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. It is only when the expert meets these requirements that he or she satisfies 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:

  1. Qualifications
  2. Reliability
  3. Helpfulness
  4. Foundation

We have attempted to briefly summarize these four pillars in this post:

1. Qualifications

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 in better understanding the evidence. The expert’s knowledge 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.

2. Reliability

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 commonly used in the field
  • appropriate application of the principles and methods

The expert’s testimony is admissible so long as the expert uses unambiguous data and follows the standard of practice in his or her field of expertise.

3. Helpfulness

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. Making sure that there is no analytical gap in his or her reasoning, the expert must provide information that is new and not obvious to the jury.

4. Foundation

The expert’s opinion must be based on foundational facts. Such facts are agreed upon by other experts in the same field. Thus, the facts from which the expert derives his or her conclusion must be accurate and pertinent to the issue of the case.