An expert witness is an individual who by virtue of education, profession, or experience, is believed to possess special knowledge of a subject beyond that of the average person, sufficient that he can testify on matters related to that subject in a court of law. For example, a doctor can serve as an expert witness in a medical malpractice lawsuit, or an engineer who specializes in accident reconstruction can testify in court regarding the causes of an automobile accident. An expert witness, is permitted to state his or her opinion concerning technical matters even though he or she was not present at the event. For example, an arson expert witness could testify about the probable cause of a suspicious fire. An expert witness testifies at a trial because they have special knowledge in a particular field. Non-expert witnesses are only permitted to testify about facts they observed and not their opinions about these facts. In family law trials, a common expert witness includes: Actuaries, who testify about values of spouses' pension plans for the purpose of dividing them at divorce; Child psychologists or development specialists, who testify about the best interests of the child when custody or visitation is in dispute; Appraisers, who testify about property values when the parties cannot agree, and; Career counselors, who testify about a homemaker's ability to return to the work force for the purpose of determining the amount and duration of alimony.