An expert qualified by the court and called as a witness at trial to state her opinion and its basis and to undergo cross examination. One acknowledged to have special training and knowledge of a particular subject, and testifying on that subject.
An expert witness has been defined as a person who possesses knowledge not within the ordinary reach and who, because of this knowledge is specially qualified to speak upon a particular subject. Steele v. Shepperd, 411 Pa. 481, 192 A.2d 397 (1963) It is not necessary that the witness possess all the knowledge in his special field of activity. However, the witness must have a reasonable pretension to specialized knowledge on the subject under investigation. Kuisis v. Baldwin-Lima-Hamilton Corp., 457 Pa. 321, 319 A.2d 914 (1974).