Commentary

This is a time of riches for those interested in the epidemiology of psychiatric disorders in childhood and adolescence. In this paper Costello and colleagues present data from the Great Smoky Mountains Study in the United States. We have also recently seen data from large epidemiological studies in New Zealand¹ and Great Britain.² This study provides an important longitudinal perspective on the changes in psychiatric presentation from age 9–16 years. It is particularly interesting in the way in which it examines comorbidity and continuity of disorders across time. It is conducted in a predominantly rural, white area of America, but there is some overlap between the findings of this study and others, suggesting that the findings may generalise to other settings.

Three findings in particular catch the eye. Firstly, the relatively low levels of Attention Deficit Hyperactivity Disorder (ADHD) found (0.9% across this age range). Secondly, the high level of comorbidity—particularly between depression and anxiety—is striking, as is the high level of continuity of disorder (homotypic continuity), and between disorders (heterotypic continuity), over time, again particularly between depression and anxiety. Finally, girls seem particularly at risk of continuing psychiatric disorder once they have developed one, and at higher risk of developing another psychiatric disorder. This finding in particular represents a challenge to clinical practice—that although girls have a lower risk of psychiatric disorder overall, when they do develop a disorder it seems that they should be considered at special risk of further disorder. When these findings are considered, together with those from New Zealand,¹ an important public health message emerges. The roots of much adolescent (and adult) psychiatric disorder begin in childhood, with psychiatric disorder in younger years carrying a significant risk for adverse psychiatric outcomes throughout life.