Participants were from the Longitudinal Twin Study (LTS) and Community Twin Study (CTS), two community-based twin samples, assessed as a part of the Center on Antisocial Drug Dependence (CADD). The LTS twins were recruited through the Colorado Department of Health's Division of Vital Statistics and were included in the CADD sample as they reached their 12th birthday. Twins from the CTS were recruited through the Department of Health and 170 out of 176 school districts in Colorado. Since these samples were community based twin samples and not selected on religiosity or alcohol related phenotypes, combining the two into one large sample was permissible. Data were available for 2754 individual twins at time 1 (male = 1311, female = 1443), and 2486 individual twins at time 2 (male = 1153, female = 1333). These individuals comprised 689 identical, or monozygotic (MZ), twin pairs (male = 311, female = 378), and 740 fraternal, or dizygotic (DZ) twin pairs (male = 230, female = 235, opposite sex = 275), for whom data were available for at least one twin at one or more
