“…Custom is determined primarily through the testimony of experts in the same field as the defendant, although some encapsulations of expert opinion, such as practice guidelines, may also be used. 5,6 In at least 20 states, there has been a discernible shift in recent years away from custom and toward a more independent determination by the court of whether the defendant deviated from "reasonable" conduct. 7 There are three social goals of malpractice litigation: to deter unsafe practices, to compensate persons injured through negligence, and to exact corrective justice.…”