Background: Attention-Deficit/Hyperactivity Disorder (ADHD) is one of the most prevalent child psychiatric disorders and represents challenges for the individual, family members, and society. Previous research has shown that individuals with ADHD often have difficulties with executive functioning (EF), an umbrella term for cognitive abilities involved in goal-directed behaviors and regulation of emotion, and that the majority of individuals with ADHD have co-occurring psychopathology such as anxiety or conduct disorder. Less is known about the relationship between EF and co-occurring psychopathology in individuals with ADHD, as well as the impact of early EF difficulties and co-occurring psychopathology on adult outcomes. The first aim of the dissertation was to examine the developmental trajectories and outcomes of individuals with ADHD from childhood to emerging adulthood in terms of everyday functioning, decision-making, and quality of life. The second was to examine how EF difficulties, core ADHD symptoms, and co-occurring psychopathology symptoms influence developmental trajectories and outcomes.
Method: The sample comprised 173 participants at baseline (Mean age = 11.7 years, 64% males). The 173 participants included 85 individuals with ADHD, 38 with autism spectrum disorder, and 50 typically developing (TD) individuals. The participants were reassessed at 2-year (Mean age = 13.8 years) and 10-year (Mean age = 21.4 years) follow-ups. At each assessment, participants underwent testing with a comprehensive neuropsychological test battery and diagnostic (re-)assessment. The participants and their parents also completed scales on core symptoms, co-occurring psychopathology symptoms, everyday functioning, and, at the 10-year follow-up, quality of life.
Results: In Paper I, we found that baseline EF difficulties significantly predicted more co-occurring psychopathology symptoms at 2- and 10-year follow-ups, beyond the effect of ADHD symptoms. In Paper II, we found that the ADHD group displayed less improvement on a neuropsychological test of decision-making from the 2-year follow-up to the 10-year follow-up, compared to the TD group. There were no significant differences in alcohol and substance use. Furthermore, poorer baseline decision-making performance and externalizing symptoms significantly predicted self-reported risky behavior at the 10-year follow-up. In Paper III, we found that the ADHD group reported more functional impairments and lower quality of life at the 10-year follow-up compared with the TD group, but after correction for multiple comparisons, there was no significant difference between the ADHD and the TD group in self-concept. Furthermore, more internalizing symptoms and ADHD symptoms at baseline and the 2-year follow-up predicted more functional impairments and lower quality of life at the 10-year follow-up. In Paper IV, we found that within-person improvement in EF from baseline to the 2-year follow-up was associated with a decline in anxiety symptoms over the same period, whereas improvement on a test of cognitive flexibility was associated with a decline in depressive symptoms over the same two-year interval. Furthermore, we found that depressive symptoms increased with age from baseline to the 10-year follow-up.
Conclusions: The findings in this dissertation suggest that children and adolescents with ADHD continue to struggle with functional impairments, lower quality of life, and more depressive symptoms in emerging adulthood than TD individuals. However, individuals with ADHD displayed relative strengths in the domains of alcohol and substance use and selfconcept. They did not report higher alcohol and substance use than TD individuals and their self-concept was similarly good. EF, decision-making, and co-occurring psychopathology symptoms were at least as important predictors of developmental trajectories and outcomes as ADHD symptoms. Therefore, factors such as EF, decision-making, and co-occurring psychopathology are important to consider in clinical care and interventional efforts for children and adolescents with ADHD