The MacArthur Adjudicative Competence Study: a comparison of criteria for assessing the competence of criminal defendants.

A set of measures assessing competence-related abilities was administered to three groups of criminal defendants: a group committed for restoration of competence, a group identified by jail personnel as mentally ill but not incompetent, and a group without identified mental disorder. Data from this study were used to test key assumptions bearing on the legal criteria for adjudicative competence. The data show that among defendants able to understand the nature and purpose of the criminal proceedings, a significant proportion have an impaired ability to appreciate their situations as criminal defendants or to communicate relevant information to counsel; among defendants able to understand the proceedings and to assist counsel, a significant proportion have impaired decision-making abilities; and among defendants able to understand the nature and consequences of decisions to plead guilty or waive a jury, a significant proportion have impaired abilities to appreciate the significance of these decisions or to rationally manipulate information pertinent to making them. These findings highlight the importance of disaggregating the components of adjudicative competence.