A Mixed Methods Examination of the Impact of Clark v. Arizona

The United States Supreme Court decision in Clark v. Arizona has become a fundamental part of the landscape concerning the insanity defense and, as a result, has greatly impacted the general use of mental health evidence. In particular, Clark and its progeny have effectively narrowed the scope and significance of mental health evidence used at criminal trials for the state of Arizona and many other states which follow a similar model. This has the net effect of limiting or even eliminating potential defenses and evidence to be considered as a mitigating factor for mentally ill defendants during the guilt phase of trial. Yet, to date, there has not been a study which has examined the impact of Clark on how courts handle mental health evidence or the insanity defense. This dissertation seeks to fill the gap in the literature by systematically reviewing all state and federal criminal cases which have cited the Clark decision through January 1, 2023. During the study period 175 cases were examined using a mixed methods research design. The results indicate that Clark has created an unworkable standard for courts. Specifically, courts have problems properly applying Clark to evidence regarding behavioral tendencies. The data suggests that when behavioral-tendency evidence is even only somewhat linked to a serious mental illness, courts are categorizing this evidence as diminished capacity evidence and excluding it from being admitted in jurisdictions that do not recognize that defense. In addition, courts have issues properly applying their state’s test for the insanity defense. The results suggest that some courts are erroneously conflating purposeful action with appreciation of the wrongfulness of the act.