The MacArthur Treatment Competence Study. III: Abilities of patients to consent to psychiatric and medical treatments.

Three instruments assessing abilities related to legal standards for competence to consent to treatment were administered to 6 groups: patients recently hospitalized for schizophrenia, major depression, and ischemic heart disease, as well as three groups of non-ill persons in the community who were matched with the hospitalized patients on age, gender, race, and socioeconomic status. Significant impairments in decisional abilities were found for only a minority of persons in all groups. Both the schizophrenia and depression groups manifested poorer understanding of treatment disclosures, poorer reasoning in decision making regarding treatment, and a greater likelihood of failing to appreciate their illness or the potential benefits of treatment. Deficits were more pronounced, however, among patients with schizophrenia. Implications are discussed for policy designed to protect the rights and welfare of patients with mental illness who are at risk of incompetent refusal or consent when making treatment decisions.