Criteria for ODD or CD were met at one or more study contacts by 19.1% of boys and 9.6% of girls between the ages of 9 and 16 years: CD was diagnosed on at least one occasion in 8.6% of youth (3.7% girls, 13.2% boys), and ODD in 9.7% (7.8% girls, 11.6% boys). We used a variety of approaches to assess whether ODD constituted a developmental precursor to CD, beginning with comparisons of age at first symptom onset. We found that ODD disorder was generally reported to onset earlier in development than CD. Median age at first symptom onset for cases of ODD was 2.5 years. CD first symptom onset was a full three years later, at 5.5 years. Despite these marked differences in overall ages at symptom onset, ODD symptoms preceded CD symptoms in only 56.0% (95% Confidence Interval (CI): 43.6, 67.4) of CD cases.
