Using an epidemiological approach to investigate sex differences in the manifestation of ADHD in youth and adulthood

Student thesis: Doctoral ThesisDoctor of Philosophy


Attention-deficit/hyperactivity disorder (ADHD) is a common and impairing neurodevelopmental disorder, defined by maladaptive levels of inattentive and hyperactive/impulsive behaviours. In youth, more males than females receive a diagnosis and the literature is clear in identifying that females with ADHD may be underdiagnosed compared to males. The sex ratio balances out in adulthood, but the diagnosis in adulthood is less common in comparison to youth and is based on age-appropriate adaptations of behavioural symptom descriptions developed to reflect ADHD in childhood. Research has uncovered a wider range of traits that are characteristic of the disorder and could form part of the core symptomatology, which have the potential to aid diagnosis in adults, such as excessive spontaneous mind wandering.
In this thesis, I capitalise on the strengths of epidemiological datasets to investigate sex differences in ADHD across the lifespan and aim to uncover factors that may influence differential referral and diagnostic rates. The first two empirical chapters examine sex differences in youth. Specifically, I examine whether different factors are associated with meeting diagnostic criteria in females versus males, whether sex-dependent biases in parental perceptions of ADHD symptoms exist, and whether the predictive associations of symptoms on being diagnosed and treated for ADHD differs in males and females. The last two empirical chapters investigate ADHD in adulthood and whether a new measure based on the internal subjective experience of ADHD symptoms - excessive mind wandering - could have clinical utility in ADHD diagnosis and add to our understanding of sex differences in the manifestation of ADHD.
My findings suggest that females’ ADHD symptoms may need to be made more prominent by additional behavioural and emotional problems for them to receive clinical recognition for their ADHD, and that in the absence of prominent externalising problems females may be more easily missed in the ADHD diagnostic process. Furthermore, sex differences in parental perceptions of ADHD behaviours and impairment were demonstrated, indicating that parents may be less sensitive to ADHD symptoms and impairment in females which could lead to under-referral. My findings also suggest that excessive mind wandering is a common co-occurring feature of adult ADHD that has specific effects on impairment, and that a newly developed measure of mind wandering - The Mind Excessively Wandering Scale (MEWS) – could have clinical utility as an additional screening tool in adult ADHD assessment and be used for treatment monitoring. Moreover, that the pattern of sex differences observed for the behavioural symptoms of ADHD in youth and adulthood are also reflected in the internalised and subjective experience of excessive mind wandering in adulthood.
It is a public health concern if individuals with ADHD are being missed and not gaining access to services and treatment that they could benefit from, and thus are at greater risk for the adverse outcomes associated with ADHD. Overall, the results of this thesis highlight the need for a careful approach in the assessment of individuals with symptoms of ADHD, specifically females and adults. More research is needed to interrogate further the reasons why females with ADHD may be under-referred and under-diagnosed.
Date of Award2019
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorPhilip Asherson (Supervisor), Fruhling Rijsdijk (Supervisor), Jessica Blais (Supervisor) & Grainne McLoughlin (Supervisor)

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