Abstract

Child psychological disorders co-occur at a much greater rate than would be expected by chance. Comorbidity is known to occur both within and across diagnostic classes, such that even disorders lying at opposite ends of the diagnostic spectrum (i.e., internalizing and externalizing disorders) commonly co-occur. Although patterns of concurrent comorbidity have been widely studied, relatively little is know about how internalizing and externalizing disorders co-occur and influence one another over time.

The overall aim of this research was to investigate patterns of sequential comorbidity in a community-based sample of children, followed longitudinally from age 3 to age 16. Data was drawn from the Concordia Longitudinal Risk Project, a prospective, intergenerational study of children from disadvantaged neighborhoods (Study 1: N = 154; Study 2: N = 143). Three pathways to comorbidity were considered: 1) that symptoms of internalizing and externalizing disorders influence one another over time; 2) that common temperament risk factors are implicated in the co-development of internalizing and externalizing problems; and 3) that disorders co-occur over time because of the high degree of symptom overlap across disorders. Study 1 examined longitudinal patterns of internalizing and externalizing problems, finding an inhibitory effect of internalizing problems on the development of future externalizing problems. Results demonstrated that the presence of common risk factors (i.e., temperamental negative emotionality) best explained the co-occurrence between internalizing and externalizing problems and additionally, unique temperamental risk factors (i.e., sociability, activity) predicted their differentiation. Study 2 examined patterns of sequential comorbidity within the diagnostic class of internalizing disorders (i.e., anxiety and depression). Results from this study indicated a sequential progression from anxiety to depression, but that this association was primarily attributed to symptom overlap among questionnaires used to assess anxiety and depressive symptoms. Instead, the co-occurrence between anxiety and depression (at both the symptom and diagnostic level) was best explained by a common temperamental style characterized by high negative emotionality and low positive emotionality. Additionally, both studies revealed significant interactions between child characteristics (gender and temperament) and parenting in the prediction of children’s internalizing and externalizing problems.

The present studies build on previous work linking temperament and parenting practices to the development of specific childhood psychopathologies. Findings of common temperamental styles predicting the co-development of internalizing and externalizing problems across time, however, are novel. More broadly, these findings suggest that temperamental styles explain a large portion of the co-variation in symptomatology, both within and across diagnostic classes. Additionally, other temperamental styles and parenting practices, both separately and in combination, predict the differentiation of problems. These findings highlight the need for future studies to consider both concurrent and longitudinal patterns of comorbidity, as well as multiple potential pathways to comorbidity. This line of research has implications for etiology, intervention, prevention, and classification of child psychopathology.