The goals of this study were to test whether Attention Deficit Hyperactivity Disorder (ADHD) and Conduct Disorder (CD) co-occur at high rates in adolescence, to determine whether youth with comorbid (co-occurring) ADHD and CD face the poorest functional outcomes in adolescence and to identify a plausible explanation for why youth with comorbidity face a poorer prognosis than youth without it. Our study was a secondary data analysis of the Environmental Risk (E-Risk) Longitudinal Twin Study, which assessed the course of behavior disorders across 1,116 same sex British and Welsh twin pairs from when they were five until they turned 18.
We hypothesized that youth with early-onset CD (before age 10) would have more ADHD symptoms at 18 compared to youth who received a diagnosis in adolescence (between ages 10 and 18) or who were never diagnosed. We surmised that heightened deficits in executive functions, cognitive processes underlying goal and future-oriented behaviors, would explain the poor outcomes associated with comorbidity because they compromise the sustained attention, inhibition and motivation control needed to refrain from the behaviors that lead to them.
Supporting our first hypothesis our results showed that the mean number ADHD symptoms in adolescence varies based on when CD emerges: youth with early-onset CD (CD ages five – 10) had, at trend level, more ADHD symptoms at 18 compared to youth with adolescent-onset CD (ages 12–18) or no CD. While our second set of findings confirmed that youth with comorbid ADHD and CD face significantly more poor outcomes than youth without it they also indicated that executive function deficits had no effect on this relationship.
Throughout the course of this year I have learned a great deal both about psychological research and my own specific interests. My project has only solidified my interest in the etiologies, manifestations and prognoses of both neurodevelopmental and externalizing behavior disorders. It also allowed me to explore the neuropsychological underpinnings of these disorders, which has been a novel and exciting opportunity. Participating in this research project greatly enhanced my education primarily by allowing me to supplement what I have learned from clinical experiences with tangible data. I owe immense gratitude to the Center for Undergraduate Research & Fellowships at the University of Pennsylvania for their generous grant and their belief in the value of my research.