Attrition, defined as either a failure to locate the individual or his or her refusal to participate between baseline and the age-22 evaluation, was 23%. As shown in Table 1, participants who attrited were more likely to be female, have lower SES, and have lower Full Scale IQ, as measured by the Wechsler Intelligence Scale for Children WISC-III-R (1991). However, both retained and attrited participants scored in the normal range of intelligence. Importantly, the Transmissible Liability Index (TLI), the predictor variable, did not differ between retained and attrited participants. Frequency of externalizing diagnoses also did not differ between attrited and retained subjects. Thus, although the sample at the age-22 outcome evaluation contained proportionally fewer females and more participants having lower social status and intellectual capacity, their behavioral characteristics were not different from the attrited participants.
