Determining when impairment constitutes incapacity for informed consent in schizophrenia research.

BACKGROUND Although people with schizophrenia display impaired abilities for consent, it is not known how much impairment constitutes incapacity. AIMS To assess a method for determining the categorical capacity status of potential participants in schizophrenia research. METHOD Expert-judgement validation of capacity thresholds on the sub-scales of the MacArthur Competence Assessment Tool-Clinical Research (MacCAT-CR) was evaluated using receiver operating characteristic (ROC) analysis in 91 people with severe mental illness and 40 controls. RESULTS The ROC areas under the curve for the understanding, appreciation and reasoning sub-scales of the MacCAT-CR were 0.94 (95% CI 0.88-0.99), 0.85 (95% CI 0.76-0.94) and 0.80 (95% CI 0.70-0.90). These findings yielded negative and positive predictive values of incapacity that can guide the practice of investigators and research ethics committees. CONCLUSIONS By performing such validation studies for a few categories of research with varying risks and benefits, it might be possible to create evidence-based capacity determination guidelines for most schizophrenia research.