Age, psychiatry admission status and linear mental capacity for treatment decisions.

The relationship between age and mental capacity among psychiatry inpatients is not fully understood. We aimed to assess mental capacity for treatment decisions in voluntary and involuntary psychiatry inpatients in Ireland and, in this analysis of our data-set, to elucidate the linear relationship, if any, between linear (as opposed to categorical) mental capacity and age. We used the MacArthur Competence Assessment Tool for Treatment (MacCAT-T) to assess mental capacity for treatment decisions in 215 psychiatry inpatients (176 voluntary and 39 involuntary) in four psychiatry admission units in Ireland. Mean age was 46.2 years and majorities were male (58.1%), never married (74.0%), unemployed (64.2%) and of Irish ethnicity (87.0%). The most common primary diagnoses were schizophrenia and related disorders (42.8%) followed by affective disorders (36.7%). On multi-variable linear regression analysis, linear mental capacity was significantly associated with voluntary admission status, being employed, having a primary diagnosis other than schizophrenia or a related disorder, and younger age. Together, these factors accounted for 44.4% of the variance in mental capacity between participants. Overall, while increased age is associated with diminished mental capacity, other factors appear more significant, including involuntary admission status which is likely an indicator of symptom severity. There is a need for further research to (a) elucidate the relationships between the significant factors identified in this study and the cognitive status of patients (which impacts on assessments of mental capacity); (b) identify and elucidate other factors of likely relevance to mental capacity (e.g. medical illness, medication use); and (c) translate these findings into targeted interventions to support decision-making in clinical practice among psychiatry inpatients, especially those with involuntary status.