we are justified in pooling cases across these samples. In addition, the data shown in Table 3 further demonstrates that we have been highly successful in recruiting at-risk twins; 52% of the ES screened males and 41% of the screened females met criteria for a childhood disruptive disorder diagnosis at the probable or definite level. At the pair level, 63% of the screened pairs had at least one member with a diagnosis of ADHD, CD, or ODD. Combining across all samples, the addition of the ES study has effectively doubled the number of at-risk twins available for analysis (n=650). The unusually large sample of affected females (n=232) ensures that this high-risk sample is well suited for the investigation of gender effects. Moreover, by age 11, 165 twins (105 males and 60 females) were receiving pharmacological treatment for ADHD (e.g., methylphenidate), giving us a large sample with which to explore iatrogenic effects of ADHD treatment. Finally, we can expect the number of CD and ODD cases to increase when the age-14 follow-up assessment is complete.
