Concordance of mental capacity assessments based on legal and clinical criteria: A cross-sectional study of psychiatry inpatients.

This study aimed to compare assessments of mental capacity based on legal criteria with assessments based on clinical criteria among psychiatry inpatients to establish the concordance, if any, between these two approaches to assessing mental capacity. We assessed mental capacity for treatment decisions in 215 psychiatry inpatients (176 voluntary and 39 involuntary) in four psychiatry admission units in Ireland using both legal criteria (Ireland's Assisted Decision-Making (Capacity) Act 2015) and clinical criteria (the MacArthur Competence Assessment Tool for Treatment; MacCAT-T). Over one third of participants (34.9%) lacked mental capacity for treatment decisions according to the legal criteria. Mental incapacity was associated with involuntary admission status, being unemployed, a primary diagnosis of schizophrenia or a related disorder, and older age. Patients who lacked mental capacity according to the legislation scored significantly lower on all subscales of the MacCAT-T than patients who had mental capacity. We conclude that mental capacity assessments based on legal criteria correlate closely with those based on clinical criteria. These findings support current legal definitions of mental incapacity in Ireland and other jurisdictions with similar legislation (e.g. England and Wales).