We can evaluate the success of the ES recruitment strategies in two ways. First, because the recruitment and assessment of the ES unscreened sample was intended to parallel the MTFS younger cohort, we can assess the overall similarity between these two groups. Second, we can determine the extent to which we have enriched the sample for the presence of childhood disruptive disorders. Table 3 reports the number of cases and the prevalence of DSM-III-R diagnoses (the diagnostic system in place when the study began) for the MTFS younger cohort, ES unscreened, and ES screened samples, all assessed at age 11. These data are shown for ADHD, ODD, and CD, at the definite and at the definite plus probable levels. The differences in diagnostic prevalence for childhood disruptive disorders between the ES unscreened and earlier MTFS samples are negligible, suggesting that 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
