Convergence or Divergence? Comparing Mental Capacity Assessments Based on Legal and Clinical Criteria in Medical and Surgical Inpatients

Abstract

Despite the high prevalence of mental incapacity for treatment decisions in hospitals (27.7%), there is little information about the relationship, if any, between mental capacity assessments based on clinical and legal criteria. We performed a cross-sectional study of mental incapacity for treatment decisions in 300 hospital inpatients in two hospitals in Ireland, using the MacArthur Competence Assessment Tool for Treatment (MacCAT-T) and the legal definition of mental incapacity in Ireland's incoming Assisted Decision-Making (Capacity) Act 2015. We found that patients who lacked mental capacity according to the legal criteria scored significantly lower on all four subscales of the MacCAT-T (Understanding, Appreciation, Reasoning, and Communication) compared to those who had mental capacity according to the legal criteria. In light of the similarity between Ireland's legal definition of mental incapacity and legislative definitions in other jurisdictions (e.g. England and Wales), we conclude that legal assessments of mental incapacity in these countries accord closely with clinical assessments (as reflected in the MacCAT-T). Ireland's new mental capacity legislation should be implemented promptly in order to further operationalize Ireland's new legal definition of mental incapacity and provide patients with the supports they need to optimize their mental capacity for treatment decisions in hospitals.