 At this point in time, the most widely used instrument is the MacCAT-T (Grisso, Appelbaum, &amp; Hill-Fotouhi 1997). It reflects the most widely influential theory of competence to date, that of Grisso and Appelbaum (1998). At the core of this theory are the same four abilities mentioned in  §4  of this entry: the ability to communicate a choice, the ability to understand, the ability to appreciate, and the ability to reason. However, Grisso and Appelbaum (1998) develop detailed specifications for how these four abilities should be interpreted. We shall call the view of competence defined in terms of these four abilities as interpreted by Grisso and Appelbaum the “four-abilities model”. The MacCAT-T is an instrument designed to help clinicians quickly and efficiently assess competence according to the four-abilities model. Thus to ask if the MacCAT-T is empirically valid is to ask whether it is good at detecting the presence of the four abilities as specified by the model and whether it is good at measuring the degree to which a patient possesses them. A great deal of research has been done on the MacCAT-T, and at this point the general consensus appears to be that the MacCAT-T is empirically valid in this narrow sense.