Carolien Zeetsen

131 CHAPTER Summary and general discussion 7 An adjustment for the number of years of education is already implemented in the MoCA (Nasreddine et al., 2005). However, this adjustment method may not be optimal for the Dutch educational system in which level of education is a more important factor for educational attainment than the number of years of formal education (Duits et al., 2014). Therefore, the existing adjustment for years of education may not be optimal. It was found in healthy participants that performance on the MoCA is moderated by both level of education and estimated premorbid intelligence (Chapter 2), therefore, a more fine–grained adjustment for level of education is introduced in Chapter 3, in which one additional point is awarded for individuals with an average level of education and two points for individuals with a low level of education, providing a more robust solution to overcome the moderation effect of level of education. The effect of intelligence on MoCA performance was expected, as it is known that intelligence typically correlates highly with level of education in young and middle–aged adults (Lezak et al., 2012) and the effect of years of education was already demonstrated previously (Nasreddine et al., 2005; Zheng et al., 2012; Sugarman et al., 2014; Yancar Demir et al., 2015; Apolinario et al., 2018). Effect of substance use related characteristics The effect(s) of several substance–related characteristics (i.e. substance type, abstinence duration, years of regular use, polysubstance use, severity of the substance use and psychological complaints such as depressive symptoms, anxiety and stress) were also examined. Neither substance type nor abstinence duration were significant predictors of performance differences on the MoCA (Chapter 3). It should be noted, however, that the effect of age on MoCA performance was significant for patients using alcohol and cannabis, but not for other substances of abuse. Next, no relation was found between MoCA performance and any of the substance use related characteristics: years of regular use, polysubstance use, being abstinent, abstinence duration, severity of the dependence and/or abuse, and psychological complaints (depressive symptoms, anxiety, or stress). Also, in a group of patients with GUD, no relationship was found between MoCA performance and severity of GHB use (Chapter 6). The lack of relations between the MoCA–TS and psychological complaints is in line with recent findings in a sample of polysubstance users showing that the MoCA–TS was unrelated to the results on a (psychiatric) symptom checklist (Hagen et al., 2019). As for being abstinent or not, and abstinence duration, Walvoort et al. (2013) argued that a minimum period of six weeks abstinence is recommended before the intoxicating effects of alcohol in the brain are minimised and an NPA can be administered validly. However, the MoCA is a cognitive screener that may be less sensitive to the (sub) acute effects of substance use than an NPA. Furthermore, our current sample did not only consist of alcohol users.