A comparison of the impact of insanity defense standards on juror decision-making

Following the Hinckley acquittal, 17 states and the federal government have made changes to the insanity defense. Changes generally involved revising the insanity defense standard, reassigning the burden of proof, and altering the standard of proof. Several states have also introduced the Guilty But Mentally Ill verdict. Although the insanity defense has spawned a great deal of controversy, there is a paucity of research investigating the impact of various insanity defense standards on jurors\u27 findings of guilt. Most jurisdictions employ the M\u27Naghten standard or the American Law Institute (ALI) standard. The first purpose of this dissertation was to determine whether the insanity standard employed has a significant effect on mock jurors\u27 verdicts. I also investigated the effect that the burden of proof and standard of proof have on mock jurors\u27 verdicts. The results revealed no significant differences for insanity defense standard, burden of proof or standard of proof. A second study measured participants\u27 comprehension of insanity defense instructions. The factors jurors use to decide whether to find one NGRI were also assessed. Participants\u27 comprehension of elements of both the ALI and M\u27Naghten standards were very low. Participants were unable to recall which side was assigned the burden of proof better than would have been expected by chance. Finally, slightly over 50% percent of participants correctly identified the standard of evidence which was necessary to prove the insanity defense. Finally, participants were asked to identify those factors which they considered important in determining whether a defendant should be found NGRI. Only three elements of insanity defense standards were identified as being significant in participant\u27s decisionmaking. These data suggest that jurors tend not to pay much attention to the actual legal standard being employed and, instead, rely on their own beliefs about what is important in deciding whether a defendant is NGRI. The results, therefore, have important implications for policy decisions regarding the insanity defense