Expert Testimony Law and Legal Definition

Expert testimony is the testimony made by a qualified person about a scientific, technical, or professional issue. An expert is often called upon to testify due to his/her familiarity with the subject or special training in the field. To be admissible, expert testimony must concern specialized knowledge and must aid the trier of fact. The expert's opinion must be sufficiently validated, by sound reason and method. Secondly, it must be relevant to the facts at issue. The assessment of reliability is meant to be flexible and concerned more with the principles and methodology the expert employs than with his/ her conclusions. Factors bearing on the reliability of expert testimony include (1) “whether a theory or technique can be and has been tested; (2) whether the theory or technique has been subjected to peer review and publication; (3) whether, with respect to a particular technique, there is a high known or potential rate of error and whether there are standards controlling the technique's operation; and, (4) whether the theory or technique enjoys general acceptance within the relevant scientific, technical, or other specialized community.”