Participants were drawn from the 578 young men who were in the 17-year-old age cohort of the Minnesota Twin Family Study (MTFS; Iacono, Carlson, Taylor, Elkins, & McGue, 1999). The total number of participants per paternal risk group was 161 men in the low-risk group (from 87 fathers), 126 men in the intermediate-risk group (from 70 fathers), and 82 men in the severe-risk group (from 44 fathers). Participants were identified from birth records of the Minnesota Department of Health as being twins born in the state of Minnesota during the years 1972–1978. They were invited to come to the laboratories of the MTFS by phone or by mail during their senior year of high school. Details regarding the sampling approach and representativeness of the sample recruited were provided in Iacono et al. (1999) and Holdcraft and Iacono (2004). Table 1 depicts demographic data for the participants in the externalizing risk groups. In general, the data in Table 1 indicate that compared with the low-risk fathers, both the intermediate- and severe-risk fathers were less well educated and had lower levels of
