Community standards of criminal liability and the insanity defense

Two experiments (N=71) compare lay standards of insanity to standards incorporated in American legal codes. In Experiment 1, case vignettes provided only legally relevant information about defendants' degrees of impairment in cognition or in behavioral control. Respondents' judgments of criminal liability ornot guilty by reason of insanity (NGRI) reflected an exculpatory standard of substantial impairment in both cognition and control. In Experiment 2, case vignettes provided realistic information about defendants' psychiatric diagnoses; respondents had to infer levels of cognitive and control impairment. Results showed that respondents made highly idiosyncratic inferences based on diagnostic categories, but once made, these inferences predicted NGRI judgments. Implications of the concordance between laypeople's rules for assigning NGRI verdicts and the rules used in American legal codes are discussed.Daniel Bailis gratefully acknowledges the support of Public Health Service grant No. 5T32 MH18021-07 for Research Training in Social Psychology during the time in which the present research was conducted. John Darley wished to acknowledge the generous support of the John Simon Guggenheim Foundation and Princeton University. Study 2 presents work done for the Princeton University undergraduate thesis of Tracy Waxman. The authors are grateful to Norman J. Finkel, Valerie Hans, and three anonymous reviewers for comments on an earlier draft on this article.Northwestern University.