The MacArthur adjudicative competence study: development and validation of a research instrument

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.