An expert is someone who knows something beyond common experience who can help you prove something you couldn't prove otherwise. The most common expert witnesses are professionals, but there are also non-degreed experts whose background and experience qualifies them. The expert's function as teacher to the attorney and jurors is a critical one. The more persuasive he or she is, the better. In a way, an expert witness is like the anchor person on a television news program.
Some networks emphasize polished delivery.
Others rely on seasoned reporters, valuing their command of the facts over their appearance. Ideally, the anchor person is a combination of both types, and so is the expert witness. Experts from academic fields may be good communicators because of classroom practice, but they may be less available than professionals from consulting firms who can take the time necessary to be thoroughly prepared. Similarly, there are pluses and minuses to hiring experts within a company involved in litigation. On the positive side, they have generally devoted time to the issue and are less likely to be blind-sided.