An expert witness gives testimony about a scientific, technical or professional issue and is qualified to testify because of familiarity with the subject or special training in the field. Generally speaking, the law of evidence in both civil and criminal cases confines the testimony of witnesses to statements of concrete facts within their own observation, knowledge and recollection. Testimony must normally state facts perceived by the witnesses’ use of their own senses, as distinguished from their opinions, inferences, impressions and conclusions drawn from the facts. Opinion testimony that is based on facts is usually considered incompetent and inadmissible, if the fact-finders are as well qualified as the witness to draw conclusions from the facts.
Expert witnesses are people who are qualified, either by actual experience of by careful study, to form definite opinions with respect to a division of science, a branch of art or a department of trade. The law deems people having no such experience or training to be incapable of forming accurate opinions or drawing correct conclusions. Thus, if scientific, technical or other specialized knowledge will assist a judge or jury to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training or education, may testify in the form of an opinion.
Courts do not apply a rigid rule in determining whether a particular witness is qualified to testify as an expert. Instead, an expert’s qualifications are normally evaluated on a witness-by-witness basis, according to the facts and issues of each case. There are two general classes of matters as to which expert testimony is admissible. In the first class, the facts are stated by the experts and the conclusion is drawn by the jury. In the second class, the expert sets forth the facts and states a conclusion, in the form of an opinion, which may be accepted or rejected by the jury.
In medical malpractice cases, physicians may provide the jury with testimony regarding the underlying facts of the legal dispute and may aid the jury by describing the standard of care for diagnosis and treatment. The standard of care can be defined as what a normal, competent physician would have done in the same situation as what occurred in the legal dispute. The medical expert will give their opinion if the physician met that standard of care. If the standard of care was not met, the expert will also give an opinion if that failure directly led to the patient’s injury.