Expert evidence is testimony given by one specially versed or skilled in a certain science, profession, or trade, concerning information beyond the range of ordinary knowledge and intelligence. Concerning matters of science, skill, or trade, or subjects of a kindred nature, persons who have made a special study or practice thereof, and who are well versed or skilled therein, may give either their opinion thereon or testify to facts within their knowledge. Persons so versed or skilled are called "experts."

Unless the matters under investigation involve some question beyond the range of ordinary knowledge or understanding, there is no province for the introduction of expert testimony. Opinions are never received so long as the facts in the case are readily intelligible to the court and jury, nor so long as the subject under inquiry is one readily understood by men of ordinary intelligence and knowledge.

The reason for the admission of expert or opinion evidence is one of necessity, the theory of the law being that a court or jury, having given a scientific subject, or trade requiring skill, no study, and having no knowledge or experience in a subject little known to the generality of mankind, are unable to form a correct judgment concerning it. One who, by practice, or observation, or special study, has become skilled or learned therein, is better able to form an accurate opinion concerning the same.