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BACKGROUND: Is the nature of decision-making capacity (DMC) for treatment significantly different in medical and psychiatric patients? AIMS: To compare the abilities relevant to DMC for treatment in medical and psychiatric patients who are able to communicate a treatment choice. METHOD: A secondary analysis of two cross-sectional studies of consecutive admissions: 125 to a psychiatric hospital and 164 to a medical hospital. The MacArthur Competence Assessment Tool - Treatment and a clinical interview were used to assess decision-making abilities (understanding, appreciating and reasoning) and judgements of DMC. We limited analysis to patients able to express a choice about treatment and stratified the analysis by low and high understanding ability. RESULTS: Most people scoring low on understanding were judged to lack DMC and there was no difference by hospital (P = 0.14). In both hospitals there were patients who were able to understand yet lacked DMC (39% psychiatric v. 13% medical in-patients, P<0.001). Appreciation was a better 'test' of DMC in the psychiatric hospital (where psychotic and severe affective disorders predominated) (P<0.001), whereas reasoning was a better test of DMC in the medical hospital (where cognitive impairment was common) (P = 0.02). CONCLUSIONS: Among those with good understanding, the appreciation ability had more salience to DMC for treatment in a psychiatric setting and the reasoning ability had more salience in a medical setting.

Original publication




Journal article


Br J Psychiatry

Publication Date





461 - 467


Acute Disease, Adult, Cognition Disorders, Comprehension, Cross-Sectional Studies, Decision Making, Female, Hospitals, General, Hospitals, Psychiatric, Humans, Informed Consent, Inpatients, Interview, Psychological, Male, Mental Competency, Mentally Ill Persons, Middle Aged, Personal Autonomy, ROC Curve