The Mental Capacity Act allows decision-making regarding medical care and finances to be made on behalf of adults who lack the ability to make such decisions for themselves. The Act states that an adult is incapable of making a decision if they have an impairment in the functioning of their 'mind or brain' and they have a problem with understanding, retaining and/or using information pertinent to the decision, and/or a problem communicating that decision. But when it comes to establishing whether or not a person has capacity, just how much reliability is there between the verdicts of different mental health professionals. This is a little researched area, but recently Vanessa Raymont and colleagues at the Institute of Psychiatry in London and Yale University in America tested the inter-rater reliability of capacity judgements made by four consultant psychiatrists and a psychologist.

Forty in-patients on acute general medical wards were interviewed by a consultant psychiatrist using a slightly adapted version of the MacArthur Competence Assessment Tool for Treatment (MacCAT-T) – a well-established tool designed for use by clinicians – together with a vignette based measure, Thinking Rationally About Treatments (TRAT). The patients had various physical complaints including cardiovascular disease, respiratory disease or infections. Patients who clearly lacked capacity because of lack of consciousness, a complete inability to communicate, or because they were so impaired as to be unable to give their date of birth were earlier excluded from the study. The four psychiatrists and psychologist were given transcripts of the interviews, and had to decide whether or not the patients had the capacity to make a decision regarding their most recent treatment. The clinicians weren't allowed to confer.

Reassuringly, there was a high level of agreement between the five clinicians. For 77.5 per cent of the patients, the psychiatrists and psychologist were in unanimous agreement about the state of their capacity. For 22.5 per cent of the patients (i.e. nine of them) there was disagreement. Across all the patients, the average kappa score for agreement between the raters was 0.76, which means they achieved 76 per cent of the total possible agreement between their decisions, above and beyond the agreement that would be expected by chance.

The researchers said it was also reassuring that the 7 patients judged unanimously not to have capacity scored less well on the mini-mental state exam and were less likely to live independently than were the 24 patients judged unanimously to have capacity, despite this information not being available to the clinicians. This suggests the judgements of the clinicians had concurrent validity (i.e. they really were measuring mental capacity, not something else).

Writing in the International Journal of Law and Psychiatry, the researchers concluded: 'This study indicates that using transcripts from a semi-structured interview assessing capacity, experienced psychiatrists and psychologists are able to make reasonably consistent judgements, despite a heterogenous clinical population with diverse medical disorders.'

References                         

Raymont, V., Buchanan, A., David, A.S., Hayward, P., Wessely, S. & Hotopf, M. (2007). The inter-rater reliability of mental capacity assessments. International Journal of Law and Psychiatry, 30, 112-117. http://dx.doi.org/10.1016/j.ijlp.2005.09.006