Chapter 1 20 Depending on the population in which the test is administered, reliability changes. The positive predictive value (PPV) decreases and the negative predictive value (NPV) increases when there are fewer cognitive impaired patients in the studied population. For example, for the MSSE in a memory clinic, the PPV is 86% and NPV is 73%, and in general practice, the PPV is 54% and NPV is 96% (Mitchell, 2009). A test should be validated for specific populations to maintain high reliability (Rossetti et al., 2011). The reliability changes are partly due to the prevalence of the target disease in the population. However, as explained before, in old age psychiatry, the symptoms overlapmore between the diseases and, therefore, it becomes more challenging for a test to identify the target condition. It should be noted that the MoCA tests a state and not a disease. Theoriginal validation study (Nasreddine et al., 2005) uses healthy controls for comparison. Although this is often done in validation studies, it is prone to introduce bias (Davis et al., 2013; Bossuyt et al., 2015). This will especially affect the specificity, as the comparison group will have clinically unrealistically high (good) MoCA scores. Healthy controls would normally not reach out for an assessment, as they are selected to have no cognitive complaints, impairments, or any other disease that could cause cognitive complaints. Therefore, separation from the impaired group will be too optimistic. This results in unnaturalistic high specificity. In clinical practice, an assessment should identify impaired patients in a naturalistic population, who, in our case, are patients that are referred (with complaints). If the MoCA is used for screening purposes, the setting (population) is of great importance. Healthy controls are seldom included in the target population. There is since the MoCA was introduced more literature on the effects of the (study) population on cutoffs. Normative data are also available. In short, multiple studies have suggested that the original cutoff creates too many false positives, and the specificity is expected to be lower in a clinical setting (Davis et al., 2015; Carson, Leach and Murphy, 2018; Elkana et al., 2020). This was partly expected as it used healthy controls, but other parameters that influence MoCA scores have emerged besides education. The most prominent are age and social status (Pinto et al., 2018). Therefore, it is clear that the MoCA, as with other tests, should be validated in the setting and population where they are going to be used. In our case, one can debate whether this is for all referred patients to old age psychiatry or only for those suspected of having cognitive impairment.
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