What is an Expert Testimony?
Expert testimony is scientific information or opinion, given in court by an expert who is qualified through specialized education, skilled practice in his occupation, wisdom or information about the matter at issue, and membership in a professional society. The significant element is that the testimony involves (1) an occupation that has developed a specialized body of knowledge and skills and (2) a witness from that occupation who has acquired such knowledge and skills. Expert witnesses include physicians, surgeons, accountants, engineers, architects, economists, bankers, psychiatrists, and specialists in crime detection.
Laymen are permitted to offer as evidence facts acquired by seeing, hearing, tasting, feeling, or smelling. They may also offer opinions based on such facts. But a layman cannot interpret the significance of facts that he did not observe or give his opinion on them. For example, a layman can describe another person as staggering, weaving, with bloodshot eyes, and reeking of alcohol, and based on this personal observation, give a lay opinion that the man was intoxicated. But a physician, as an expert witness, could give his opinion, merely from the description and without personal observation, that such a person was intoxicated. The value of expert testimony is its acceptance in court as evidence of facts not directly observed.
Testimony by a physician who gives his opinion that a plaintiff's physical disability was caused by a defendant's negligent act carries considerable weight in court. Expert testimony, often crucial in lawsuits, is used increasingly in modern technological society.