Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Doctor of Philosophy




Stewart, Shannon L.


This dissertation addresses current issues in the conceptualization and classification of childhood mental health issues (e.g., impact of sex/age on symptoms, comorbidity, limits of traditional models). In contrast to traditional models, the importance and value of utilizing individual symptoms as primary variables of interest is presented. This first study consisted of 9565 participants (M = 12.06, SD = 3.57, 58% males). Results for youth with no history of trauma indicated sex differences in symptom expression consistent with what has been previously shown in the literature; however, a complex presentation of attention-related symptoms was identified for females. Similar sex differences were found for participants with a history of trauma; however, there were varying patterns of symptom clustering between all participant groups. Trauma-related symptoms often clustered with symptoms of other disorders. Various symptoms (e.g., impulsivity, episodes of panic, sleep concerns) are discussed as potential bridge symptoms between diagnoses.

The second study aimed to address current issues in the diagnosis and understanding of mental health concerns in participants with intellectual disabilities (n = 863, M = 12.00, SD = 3.65, 73% male). Results indicated that participants with a history of trauma displayed higher rates of all symptom categories except attention-related symptoms. The trauma group also exhibited symptom clustering that was more diagnostically complex than those without a history of trauma. The role of various symptoms in comorbidity is discussed.

The third study explored sex differences in symptoms, comorbidity and bridge symptoms using longitudinal data (n = 2661, 55% males; age at initial assessment M = 11.81, SD = 3.46; age at discharge assessment M = 12.32, SD = 3.46). Results showed significant symptom change between initial and discharge assessments for both sexes in all symptom categories. Sex differences in symptom severity were identified at both assessment times. Females exhibited a greater number of diagnoses initially and males exhibited a greater number at discharge. Females also exhibited a greater number of individual symptoms that did not change significantly between assessments. Implications for diagnosis and effective intervention are discussed. In the final chapter, the utility of the symptom-level analyses and implications for psychology and clinical practice are discussed.

Summary for Lay Audience

Mental health issues in children are a growing concern that cause financial and emotional strain on communities and families. Children’s mental health concerns also tend to continue as they get older. In fact, most mental health issues that adults experience first began before they were 18 years old. Diagnosing and treating mental health issues in children is complicated for several reasons. First, children change a lot as they grow and develop, and so do their mental health symptoms. Having a better understanding of how mental health problems change over time would improve outcomes for children and their families. This research looked at a large number of children receiving mental health services in Ontario, Canada and confirmed that the way children express mental health issues depends on their age. It also depends on whether they are boys or girls. A child’s age and sex also interact with one another to produce different mental health outcomes. This is important to know because it tells us that the best approach to diagnosing and treating mental health disorders may not be the same for boys versus girls and elementary versus high school students.

Also, the way mental health issues in children are diagnosed is constantly being researched and changes over time. This is because, unlike medical issues, mental health diagnoses are not due to a single underlying cause. Even though this is well-known, most research relies heavily on diagnoses to study mental health issues in children. Instead, the research presented in this dissertation uses individual symptoms to better understand mental health issues. By using individual symptoms, this research aimed to explain why most children with one diagnosis also very often experience symptoms of another diagnosis. For example, many children whose anxiety causes them to struggle in school or with friends also often feel sad, guilty or embarrassed as a result. Over time, this puts them at risk for mental health issues other than anxiety, such as depression. It is known to children and families that such things are related and this research aimed to better understand these symptom relationships.