Attention-deficit hyperactivity disorder (ADHD) is a common neurodevelopmental disorder that shares a high comorbidity with anxiety disorders. However, the early development of comorbid ADHD and anxiety symptoms is not well-understood. In this study, the bidirectional relation between ADHD and anxiety symptoms was examined by testing two models of the development of ADHD and anxiety comorbidity: an anxiety effects model, which posits that anxiety symptoms contribute to the development of ADHD symptoms, and an ADHD effects model, which posits that ADHD symptoms contribute to the development of anxiety symptoms. Within the ADHD effects model, parenting practices were tested as mediators of this relation. Participants included children who were 3 years old at baseline (n = 258) and their caregivers who reported on their children's ADHD and anxiety symptoms annually for 3 years. The bidirectional relation of parent-reported anxiety and ADHD symptoms was tested using a series of cross-lagged models. Results indicated that ADHD symptoms predicted later anxiety symptoms, but anxiety symptoms did not predict later ADHD symptoms. Parenting practices did not mediate the relation between ADHD and anxiety symptoms within the ADHD effects model. These findings suggest that ADHD-anxiety comorbidity may develop in part because early symptoms of ADHD contribute to the development of anxiety symptoms; future research should be conducted to elucidate the mechanisms of this relation.
Keywords: ADHD; Anxiety; Comorbidity; Longitudinal; Preschool.