A further – and possibly more salient – issue concerns the age-range covered by our observations. The 9-16 age range covered in GSMS is a crucial period for the development of antisocial behavior, but clearly does not cover the full window of risk. Many children meet criteria for disruptive behavior disorders at much younger ages, beginning in the pre-school years (Egger & Angold, 2006). This could have a number of implications for our study. First, DSM-IV indicates that ODD may be a stronger risk factor for childhood-onset (first symptom onset prior to age 10) than adolescent onset CD. Although most GSMS observations were of children older than 10, first symptom onsets were typically reported to have occurred much earlier in childhood. Applying the DSM-IV age 10 ‘rule’ the vast majority of CD cases in the sample were classified as childhood-onset. Though we did not directly observe our cases at these earlier ages, this makes it unlikely that our relatively low rate of ODD→CD progression could be explained by a predominance of adolescent-onset cases of CD.
