One common misconception of the insanity defense is that it is overused. However, an eight state study conducted between 1976 and 1987 provided evidence that "the defense was used in less then 1 percent of all criminal cases, and that it succeeded in only about one-quarter of those" (Caplan 19). "In 1982, only 52 of 32,000 adult defendants represented by the Public Defender's office in New Jersey-less then two tenths of one percent-entered the insanity plea, and only 15 were successful" (http:/www.psych.org/public_info/insanity.cfm). In addition, "states with higher rates of not-guilty-by-reason-of-insanity defenses tend to have lower success for not-guilty-by-reason-of-insanity defenses; the percentage of all defendants found not-guilty-by-reason-of-insanity is fairly consistent, at around 0.26 percent" (Chiacchia). Clearly, the insanity defense is not subject to the abuse of overuse by defendants.
Another misconception made is that the insanity defense is most often used by heinous murderers. In reality, only fourteen percent of insanity pleas in an eight state study involved murder (Caplan 19). In the state of Missouri, "twenty-five percent of insanity verdicts involved crimes such as auto theft, bad checks, and in one instance, the theft of a pen" (qtd. in Collins, Hinkebein, and Schorgl, "Insanity: myth or Fact?" sec.6).
