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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.

Assessment of competence to stand trial is a common evaluation that can have substantial consequences for defendants and the criminal justice system. Despite a voluminous literature, much remains unknown. An obstacle to progress in understanding what is better termed "adjudicative competence" is the absence of structured, standardized research measures for assessment of defendants. This article presents the legal framework, assessment strategy, instrument description, psychometric properties, and construct validation of the MacArthur Structured Assessment of the Competencies of Criminal Defendants (MacSAC-CD). The measures meet or exceed accepted indices of internal consistency, and interscorer agreement. Observed patterns of correlations among measures support the underlying theoretical structure of competence-related abilities. Moreover, the MacSAC-CD distinguishes groups of competent and incompetent defendants; reflects changes in competence status; and correlates positively with clinical judgments, negatively with psychopathology and impaired cognitive functioning, and negligibly with cynicism toward the justice system.

The legal construct of competence to stand trial, or "adjudicative competence," is based on the premise that some mentally disordered defendants have impaired abilities when compared with most defendants and that adjudication should be barred if these competence-related abilities are significantly impaired. Where the line is drawn between sufficient and insufficient abilities has important consequences: as a result of being adjudicated incompetent, defendants may be detained and treated involuntarily and their trials will be delayed. However, no studies have systematically compared the capacities of relevant groups of defendants. In this study, 84 criminal defendants--42 of whom were hospitalized as incompetent and 42 of whom were regarded as unquestionably competent--were administered three instruments measuring capacity to understand legally relevant information. Incompetent defendants performed more poorly on all measures of understanding. Twenty-eight incompetent defendants were administered the measures a second time, after restoration to competence. Restored defendants improved their performance on all measures of understanding and their performance was similar to that of normal, competent defendants.