Assessment of capacity to consent to research among older persons with schizophrenia, Alzheimer disease, or diabetes mellitus: comparison of a 3-item questionnaire with a comprehensive standardized capacity instrument.

CONTEXT: Considerable discussion surrounds issues related to the capacities of neuropsychiatric patients to consent to research, yet few empirical investigations have directly compared decisional capacity among patients with a serious mental illness with that among patients with neurologic or medical conditions. Also, as requirements for formal assessment of decisional capacity are becoming more common, there is a clear need to identify efficient screening methods.
OBJECTIVES: To compare decisional capacity among 3 diagnostic groups, and to examine the degree to which impaired understanding can be detected with a brief set of screening questions.
SETTING: Outpatient veterans hospital clinic and university-based neuropsychiatric research centers. DESIGN/ PARTICIPANTS: Cross-sectional comparison of decisional capacity among older (>/=60 years) outpatients with schizophrenia (n = 35), mild to moderate Alzheimer disease (n = 30), and type 2 diabetes mellitus (n = 36), and determination of sensitivity and specificity of a screening measure. MAIN OUTCOME MEASURES: Three-item decisional capacity questionnaire and the MacArthur Competence Assessment Tool for Clinical Research.
RESULTS: Patients with diabetes mellitus performed the best on the capacity instruments, patients with Alzheimer disease had the worst performance, and patients with schizophrenia were intermediate. However, there was considerable heterogeneity within each group. Even within diagnostic groups, the level of cognitive functioning (measured with the Mini-Mental State Examination) was generally the best predictor of decisional capacity (particularly in the understanding component). The 3-item questionnaire was sensitive to impaired understanding as measured with the MacArthur Competence Assessment Tool for Clinical Research understanding subscale.
CONCLUSIONS: Decisional capacity differed among the 3 groups; there was considerable heterogeneity even within each diagnostic group, so individualized consideration of capacity may be warranted. The level of cognitive deficits is 1 potential marker of which participants should receive comprehensive capacity evaluations, but sensitive brief questionnaires targeting key aspects of disclosed information may also provide an effective means of screening for participants warranting comprehensive capacity evaluations.