Attention-deficit/hyperactivity disorder and educational outcomes : etiology, treatment effects, and occupational outcomes

Abstract

Attention-Deficit/Hyperactivity Disorder is one of the most prevalent childhood-onset developmental disorders, and is associated with a wide range of problematic functional outcomes such as low educational attainment (EA), accidents, and unemployment. The projects in this thesis are divided into four studies that cover the outcomes of two important functional domains in ADHD during adolescence to early adulthood: education and occupation.

In study I we examine the association between ADHD, medications for ADHD and school performance at age 16, and in particular the associations between treatment length and school performance. By comparing students diagnosed with ADHD to those without, we found that ADHD is associated with lower school performance. Among students with ADHD and treated with ADHD medications prior to graduation, those treated for a longer period had higher school performance compared to those treated for a shorter period.

Study II covers the period after compulsory school into early adulthood and the association between ADHD and occupational outcomes, as well as the role of post-compulsory EA, and comorbid neurodevelopmental disorders (NDDs) and intellectual disability (ID) in these associations. We found that ADHD was associated with lower income, higher rates of unemployment, and increased risk of receiving disability pension. Lifetime EA and comorbid NDDs and IDs explained part of these associations, but comorbid NDDs and IDs explained most of the association between ADHD and disability pension. By comparing occupational outcomes before and after educational completions (secondary and university) while accounting for individual background factors, we found that EA affected income similarly among individuals with and without ADHD, while some differences were found for unemployment.

Study III examined the association between ADHD symptoms, school performance at age 16, and early unemployment. The variation in these traits and outcomes are decomposed into genetic and environmental factors, and the extent to which the associations between them share genetic and environmental origins. Similar to prior, research ADHD symptoms correlated negatively with school performance, both phenotypically, and at a genetic level. Additionally, we found that there was a positive genetic correlation between ADHD symptoms and unemployment. Our findings confirm prior findings regarding the genetic and environmental influences on school performance using register-based measures of school performance. Additionally, we provide preliminary evidence for a shared genetic liability between ADHD and occupational outcomes, independent of school performance.

In study IV we used polygenic scores (PGS) for ADHD and study their association with school performance at age 16. We examined to what extent this association is explained by PGS for EA, phenotypic ADHD symptoms, and shared familial factors using linear regression and instrumental variable (IV) analyses. We found that PGS for ADHD associated negatively with all measures of school performance. Phenotypic ADHD symptoms accounted for a small part of these associations, while PGS for EA and shared familial factors had a more marked influence. Preliminary findings from the IV analyses suggest that the polygenic liability towards ADHD may differ between different types of subjects (e.g., language versus sports).

Overall, our findings emphasize the problematic outcomes individuals affected by ADHD may face in education and occupation. Genetic and environmental factors are important in the etiology of these outcomes and they overlap with such factors involved in the manifestation of ADHD. ADHD medications potentially have beneficial effects on school performance, and EA on occupational outcomes. Education is considered one of the most important aspect of personal and economic development in modern societies, and the policy implications of the findings of study I-IV are discussed.