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Author ORCID Identifier



Open Access Dissertation

Document Type


Degree Name

Doctor of Philosophy (PhD)

Degree Program


Year Degree Awarded


Month Degree Awarded


First Advisor

Elizabeth Harvey

Subject Categories

Child Psychology


ADHD and ODD are common and impairing externalizing disorders in childhood that are often comorbid. Understanding the development of these symptoms when they first emerge is crucial for better identifying children who are at-risk for later impairment. Parents (N = 273) were recruited via Amazon’s Mechanical Turk to complete surveys about their 2-year-old, followed by surveys every six months for two years. Children’s general pattern of ADHD and ODD symptom growth were examined with latent class analyses. Temperament traits were subsequently added as covariates. Dual group-based trajectories and cross-lagged analyses examined the co-development of these disorders. Results showed 4 distinct growth trajectories for each symptom domain. Most children follow low symptom trajectories of ODD and each domain of ADHD. A small portion of children show high symptoms across time, and others show moderate or increasing symptoms. Only the hyperactive/impulsive domain of ADHD showed a declining symptoms group akin to the “terrible twos.” Temperament traits of low effortful control, high negative affect, and high surgency increased odds of membership in high symptom groups. Children with high ODD symptoms across time had a high likelihood of membership in high ADHD symptom groups; the converse was true but probabilities were lower. Finally, hyperactive/impulsive symptoms predicted ODD symptoms across time, more than vice versa, while ODD predicted inattention symptoms. The study extends the small body of literature assessing the early development of ADHD and ODD and uses DSM-based symptoms to enhance clinical utility. Findings suggest that some children with early symptoms of ADHD or ODD are at risk for continued symptomatology and developing comorbid symptoms.