We approached this issue in a variety of ways. First, like other studies (Loeber et al., 1992; Nock et al., 2007), we confirmed that retrospectively reported first ODD symptom onsets in the GSMS sample occurred very early in development, well before CD symptom criteria typically began to be met. We note, however, that earlier onset is a necessary condition for the developmental model, but is far from sufficient. Next, we confirmed that ODD symptoms at the first assessment wave were clear predictors of later CD symptoms in boys and girls, and found that wave 1 ODD diagnoses independently predicted later diagnoses of CD in boys but not girls. Finally, we evaluated the relative frequency of this particular sequence of onsets (that is, ODD preceding CD), given the range of potential onset sequences between two disorders that could, in principle, be observed.
