Age of onset, symptom threshold, and expansion of the nosology of conduct disorder for girls.

The study of conduct disorder (CD) in girls is characterized by several nosologic controversies that center on the most common age of onset, the most valid symptom threshold, and the possible inclusion of other manifestations of antisocial behavior and dimensions of personality as part of the definition of CD. Data from a prospective, longitudinal study of a community sample of 2,451 racially diverse girls were used to empirically inform these issues. Results revealed that adolescent-onset CD is rare in girls. There was mixed support for the threshold at which symptoms are associated with impairment: Parent-reported impairment provided the clearest evidence of maintaining the current Diagnostic and Statistical Manual of Mental Disorders (4th ed.; American Psychiatric Association, 1994) threshold of 3 symptoms. The impact of callousness and relational aggression on impairment varied by informant, with small effects for parent- and youth-reported impairment and larger effects for teacher-rated impairment relative to the effects for CD. These results support arguments for revising the typical age of onset of CD for girls but for maintaining the current symptom threshold. The results also suggest the need to consider subtyping according to the presence or absence of callousness. Given its content validity, relational aggression requires further study in the context of oppositional defiant disorder and CD.