Exploring Autism, ADHD, and their Overlap, and Relationships with Mental Health and Quality of Life in UK Adults

Student thesis: Doctoral ThesisDoctor of Philosophy


Autism spectrum disorders (henceforth autism) and attention-deficit/hyperactivity disorder (ADHD) are conceptualised as common neurodevelopmental conditions. Autistic individuals are typically described as having difficulties with social interaction and communication, and unusual behaviours and interests which may be rigid and repetitive. Individuals with ADHD are typically described to have difficulties related to attention, hyperactivity and impulsivity unusual for their age and developmental level. Past research has identified that autism and ADHD commonly overlap so that autistic individuals are more likely to have ADHD than others (and vice versa). This overlap can also be seen in the dimensional traits related to autism and ADHD, so individuals with higher levels of autistic traits may also be more likely than others to have higher levels of ADHD traits.

Autistic individuals and those with ADHD (or high levels of these traits) are high priority groups for research, as existing evidence suggests that these individuals are more likely to experience a number of negative outcomes in adulthood, including poor mental health and quality of life (QoL). Both autism research and ADHD research has primarily focused on childhood and adolescence, to date, with comparatively little research into the experiences and perspectives of adults. Subsequently, research considering autism and ADHD together in adulthood is much more limited than research in childhood and adolescence. Furthermore, even less is known about how the intersection between autism and ADHD relates to mental health and QoL in adulthood. The aim of this thesis is to address this under-researched topic.

Chapter 1 presents an overview of autism, ADHD and their overlap, with a particular focus on existing research into how these are related to mental health and QoL in adulthood. Research in these areas has been relatively limited to date, and there are several conflicting findings and areas yet to be explored.

Chapters 2 and 3 use data from the Individual Differences in EEG in Young Adults Study (IDEAS), a community-based sample of young adult twins enriched for those with high autistic and/or high ADHD traits. These chapters explore whether depression, anxiety (Chapter 2), and QoL (Chapter 3) are linked to high autistic traits, high ADHD traits and their interaction in young adulthood.

Chapters 4-6 utilise data from the Quality of Life During COVID-19 (QoLVID) Study, an online volunteer sample of neurodiverse UK adults, collected during the first wave of the coronavirus pandemic. Chapters 4 and 5 explore differences between four groups of adults during the pandemic: neurotypical adults, autistic adults, neurodivergent but not autistic adults, as well as those with overlapping autistic and other neurodivergent identities. Chapter 4 examines differences between these groups in depression, anxiety, QoL and loneliness and whether participants felt these had changed due to the pandemic. Chapter 5 examines participant perceptions of the overall impact of the pandemic and the variety of changes and pandemic-related events that participants had experienced. Chapter 5 also explores, qualitatively and quantitively, the range of coping strategies that participants described using during the pandemic and the sorts of supports they felt would be helpful for them following COVID-19.

Chapter 6 aims to partially replicate analyses from Chapters 2 and 3 using data from the QoLVID sample. Therefore this chapter explores whether depression, anxiety and QoL are linked to autism, ADHD and their interaction in a convenience sample of UK adults surveyed during the pandemic.

Overall, the findings in this thesis highlight that autism and ADHD (or traits of these) are associated in an additive fashion with poorer mental health and QoL for the majority of measures used. Furthermore, a number of these findings may be particularly important as the same relationships were identified before and during the pandemic despite a large number of study design differences. In contrast, intersections between autism and other neurodivergent identities more broadly (not just ADHD) were less likely to be associated with poorer QoL and mental health.

Finally, Chapter 7 offers a general discussion of the findings presented in this thesis. This Chapter includes a summary of the main findings and a discussion of key implications and directions for future research. The limitations of this body of work are considered, and general conclusions are drawn.
Date of Award1 Jun 2022
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorFrancesca Happe (Supervisor), Grainne McLoughlin (Supervisor), Jessica Blais (Supervisor) & Emma Colvert (Supervisor)

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