We found that specific capacity assessments by the treating clinician using the ACE and SMMSE scores both agreed closely with expert assessments of patient capacity to consent to treatment. Our results complement and extend the results of previous studies of specific capacity assessments. The MacCAT-T, a specific capacity assessment, had excellent reliability when administered to schizophrenic and schizoaffective patients and normal volunteers by two trained researchers and an expert assessor.9
The Competency Interview Schedule had good reliability when administered to depressed patients by two trained research assistants.7
We have extended these results by showing that trained medical students and residents can reliably administer a specific capacity assessment to medical patients undergoing a broad range of treatment decisions, and these assessments agree closely with expert assessments.
We also found that general impressions by the supervising staff physicians agreed less closely with the expert assessments than ACE assessments by the research nurse. This supports previous observations that general impressions do not agree closely with expert assessments of capacity,3
except in patients who are obviously capable.14
The ACE and the SMMSE both agreed closely with the expert assessments, so clinicians will have to base their choice of capacity assessment method on other considerations. An important drawback of the ACE was the tendency to yield indeterminate results of probably incapable or probably capable. These results significantly altered the likelihood of incapacity, but there were too many misclassifications to allow a definite conclusion regarding incapacity.
A major strength of the ACE is its contribution to the consent process. During an ACE assessment, the clinician provides relevant treatment information to the patient, and asks open-ended questions to ensure that the information has been understood. The clinician also probes the patient’s reasons for accepting or refusing treatment. If the patient is ultimately found to be capable, this dialogue is a necessary and important component of a valid consent.
Although we only studied a single ACE assessment, we noticed that it often identified particular areas of uncertainty that could be further explored in subsequent assessments. For example, if the clinician was uncertain that the patient was able to appreciate the consequences of refusing treatment, a second interview focusing on those consequences might resolve any uncertainty regarding the patient’s capacity.
The SMMSE has several strengths, including its widespread clinical use and its tendency to yield fewer indeterminate results than the ACE. However, we cannot recommend using the SMMSE alone for capacity assessment because the SMMSE is not a useful component of the consent process. If the SMMSE result indicates that the patient is capable, the clinician will still need to engage the patient in a dialogue in which relevant information is exchanged and understanding is ensured. If the SMMSE result is indeterminate, the clinician will not have gained any useful clues to resolving this uncertainty. Both of these limitations of the SMMSE are strengths of the ACE approach.
Another limitation is that the SMMSE does not assess a person’s decision-making abilities, so it may be a less useful measure of capacity for patients with psychosis, depression, or frontal lobe disease.24
Our study population did not include many patients with psychosis, but one patient with an SMMSE score of 30 was incapable, because his refusal of dialysis was based on a delusion.
On the basis of these considerations, we recommend that clinicians perform both an ACE and an SMMSE as the initial step in assessing patient capacity to consent to treatment. The prospectively evaluated combination of ACE and SMMSE yielded fewer indeterminate results than the ACE alone, and avoids the limitations of using the SMMSE alone.
Our study had several strengths. First, we developed a rigorous reference standard using two independent experts and an independent adjudication panel. Our approach is more rigorous than previous studies of capacity to consent to treatment, which used single experts,7, 10, 25
single panels of experts,10
or statistically derived cutoff scores on questionnaires using hypothetical treatment decisions.3, 26
Clinicians often rely on the opinion of a single expert capacity assessment, so our study also used a more rigorous approach than would occur in usual practice. We recognize that our two experts may occasionally have both been wrong, or that a different adjudication panel may have reached different conclusions. We acknowledge that court hearings would have been the ideal reference standard, but court hearings are not available for research purposes.
A second strength of our study was the challenging spectrum of patients enrolled. We specifically sought patients for whom the issue of capacity was important and uncertain, while we specifically excluded patients for whom the issue of capacity was unimportant or obvious.
There are some potential limitations to our methods. First, ACE assessments were not completely independent of expert B, because expert B developed the ACE and conducted the ACE training sessions, so the close relation between expert B and the ACE assessments could be partially explained by bias. However, expert A was unaware of the content of the ACE and the results of ACE assessments, and we found a close agreement between expert A and the ACE assessments. Similarly, expert A was aware of SMMSE results, so the agreement between expert A and SMMSE results could be explained by bias. However, expert B was unaware of SMMSE results, and the agreement between SMMSE and expert B was the same as that between SMMSE and expert A. Therefore, we do not believe that our results can be explained by bias.
Another limitation relates to our study population. The majority of our study population was of North American or European descent. Nonparticipants were more likely to be refusing treatment and disagreeing with their physicians, suggesting that the therapeutic relationship was problematic.20
Capacity assessments may be less reliable if cultural or linguistic barriers are present, or if the therapeutic relationship is problematic.
Finally, the medical residents and students who conducted the ACE assessments received a 1-hour training session as part of the study. They were encouraged to conduct their ACE assessments to the best of their ability, and most of them were enthusiastic. The training, encouragement, and enthusiasm all made important contributions to the study results. However, we believe that any motivated clinician can learn to do an ACE assessment at the same level as the students and residents in our study. (The content of the training session is available from the corresponding author.)
In summary, our study demonstrates that specific capacity assessments by the treating clinician using the ACE and SMMSE scores agree closely with expert assessments of patient capacity to consent to treatment. Clinicians can use these practical, flexible, and evaluated measures as the initial step in the assessment of patient capacity to consent to treatment.