A set of measures assessing abilities related to legal standards for competence in the adjudicative process were administered to mentally-disordered criminal defendants with diagnoses of schizophrenia, affective disorder, other psychiatric disorders, and to criminal defendants without diagnosed mental disorder. Mentally-disordered defendants were recruited from two groups: those who had been committed for restoration of competence and those who had been identified by jail personnel as mentally ill. Significant impairments in competence-related abilities were found for approximately half of the defendants with schizophrenia. Defendants with schizophrenia scored lower on measures of understanding, reasoning, and appreciation related to the adjudication process. The association between symptoms and competence-related abilities was explored within diagnostic groups. Conceptual disorganization was found to be inversely correlated with performance on all measures in both defendants with schizophrenia and those with affective disorders. For other psychotic symptoms, differing patterns of correlations were found in the two major diagnostic groups. The implications for policy designed to safeguard the rights of defendants to be tried while competent are discussed.

Richard J. Bonnie et al., The MacArthur Adjudicative Competence Study: Diagnosis, Psychopathology, and Competence-related Abilities, 15 Behavioral Sciences & the Law 329–345 (1997).