When does decisional impairment become decisional incompetence? Ethical and methodological issues in capacity...

Most decision-making capacity (DMC) research has focused on measuring the decision-making abilities of patients, rather than on how such persons may be categorized as competent or incompetent. However, research ethics policies and practices either assume that we can differentiate or attempt to guide the differentiation of the competent from the incompetent. Thus there is a need to build on the recent advances in capacity research by conceptualizing and studying DMC as a categorical concept. This review discusses why there is a need for such research and addresses challenges and obstacles, both practical and theoretical. After a discussion of the potential obstacles and suggesting ways to overcome them, it discusses why clinicians with expertise in capacity assessments may be the best source of a provisional "gold standard" for criterion validation of categorical capacity status. The review provides discussions of selected key methodological issues in conducting research that treats DMC as a categorical concept, such as the issue of the optimal number of expert judges needed to generate a criterion standard and the kinds of information presented to the experts in obtaining their judgments. Future research needs are outlined.