Prevalence and correlates of adequate performance on a measure of abilities related to decisional capacity: Differences among three standards for the MacCAT-CR in patients with schizophrenia
Introduction
In recent years, there have been frequent suggestions that, in at least some contexts or for certain clinical populations, investigators should systematically evaluate whether potential research participants are competent to consent (National Bioethics Advisory Commission, 1998, UCSD Human Research Protections Program, 2004). The MacArthur Competence Assessment Tool for Clinical Research (MacCAT-CR) (Appelbaum and Grisso, 2001) is generally recognized as the best of currently available scales for this purpose (Dunn et al., 2006c, Sturman, 2005); it is also the most widely used in empirical research on consent capacity (Jeste et al., 2006, Vellinga et al., 2004).
Adequate performance on the MacCAT-CR was used in one large-scale clinical trial as part of the criteria for independent consent (Stroup et al., 2003). In most studies, however, capacity assessment has been limited to asking participants a few questions about their understanding of the study. Even in the aforementioned trial, the inclusion criteria focused solely on the MacCAT-CR Understanding subscale, without considering the other three generally recognized dimensions of decisional capacity (Appelbaum and Roth, 1982) also measured on the MacCAT-CR (appreciation of the significance of the information, reasoning with the information, and expressing a choice).
Because of the contextual nature of decisional capacity (Saks et al., 2006), the MacCAT-CR has no established cut-score or algorithm for categorical determinations of capacity or incapacity. This is appropriate, as studies vary in level of risk and in the risk/benefit ratio. General consensus exists that as the degree of risk increases, a higher level of capacity is desirable (Roberts and Dyer, 2004). Thus, no particular level of ability is determinative of adequate capacity in all circumstances (Appelbaum and Grisso, 2001). Moreover, scores on capacity assessment instruments, though helpful, should generally be supplemented with other important information, such as mental status and decision-making context (Appelbaum and Grisso, 2001).
Moreover, discussion of cutpoints is inseparable from considerations of capacity assessment serving a screening function, and from growing evidence regarding educational interventions for enhancing consent. Substantively inadequate responses to MacCAT-CR items indicate a need for further consideration of an individual's decisional abilities, and perhaps for intervention prior to enrollment—rather than as justification for making a definitive categorical decision about decisional capacity. Given that healthy controls often score less than perfectly on the MacCAT-CR (Jeste et al., 2006), perfect MacCAT-CR performance would be an untenable criterion. Rather, each investigator (and/or institutional review board, or IRB) must make some a priori decisions about what level and type of performance constitute “adequate” or “inadequate” performance, raising several key questions: how much understanding is “enough”? Are certain items particularly critical? Even when understanding is adequate, what weight should be given to a less-than-perfect performance on appreciation and/or reasoning?
These issues go beyond application and interpretation of the MacCAT-CR, reflecting genuine lack of consensus regarding what defines adequate consent capacity and under what conditions. Absent such consensus, or empirical or regulatory guidance, investigators and IRBs may make idiosyncratic decisions that may not represent a contextually appropriate balance among the goals of protecting potentially vulnerable persons, fostering important research, and respecting individuals' decision-making autonomy.
The goal of the present study was to evaluate the effects of altering some of these factors (requisite level of understanding, and additional consideration of appreciation and reasoning) on the determination of “adequate" performance on one measure related to decisional abilities (the MacCAT-CR). Although no single cut-score or algorithm on the MacCAT-CR is likely to be appropriate across all protocols or populations, there have been several MacCAT-CR cut-scores published in the literature for specific contexts (Carpenter et al., 2000, Kim et al., 2001, Stroup et al., 2005). We applied these three criteria to our sample to document the extent of disparity in the proportion of subjects categorized as having inadequate performance, and the specific sources of discrepancies under the three criteria. Our goal was not to validate any of these for general use, but rather to make explicit the sources of disagreement to foster discussion and stimulate further empirical research regarding the dimensions and degree of decisional capacity appropriately viewed as essential under differing circumstances.
Section snippets
Participants
Included 91 individuals, aged ≥ 50 years, with schizophrenia (n = 58) or schizoaffective disorder (n = 33), enrolled in a larger study on informed consent and capacity to consent to research among older persons with psychoses. Inclusion criteria were: DSM-IV diagnosis of schizophrenia or schizoaffective disorder (determined by the patient's clinician), current age ≥ 50 years, fluency in English, and the absence of a diagnosis of dementia. Recruitment sources included board-and-care residences, county
Results
Demographic characteristics, MacCAT-CR subscale scores, psychopathology ratings, and cognitive test scores are shown in Table 1. The mean psychopathology rating scales and cognitive scores suggest on average participants had mild symptoms, and mild-to-moderate cognitive impairment.
Using the standards of MacCAT-CR Understanding > 15 and Understanding ≥ 20, 92.3% and 81.3% of participants had adequate performance, respectively, but under the multidimensional standard incorporating Appreciation and
Discussion
Different standards for MacCAT-CR performance resulted in substantially different proportions of individuals with schizophrenia or schizoaffective disorder being categorized as having adequate or inadequate MacCAT-CR performance. Fully half of this sample of middle-aged and older people with schizophrenia and schizoaffective disorder fell into a gray zone of performance—“adequate” by the least stringent standard but “inadequate” by the more stringent and multidimensional standards. Adding
Acknowledgments
This work was supported by NIMH grants MH66062, MH66248, MH64722, by the National Alliance for Research on Schizophrenia and Depression, and by the VA San Diego Healthcare System. These data have been presented in part at the 2005 Annual Meeting of the American College of Neuropsychopharmacology, and at the 2006 Annual Meeting of the American Association for Geriatric Psychiatry.
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