The full sample (N= 7548) consisted of 55.8% males (mean age = 37.1, s.d. = 9.1) and 44.2% females (mean = 36.5, s.d. = 8.5), 5.5% of whom (N= 415) reported never having tried alcohol in their life. These subjects were excluded from all subsequent analyses so that our functional sample was n = 7133. An additional 3204 of the twins did not meet any of the screening criteria required to be given the full alcohol interview section and were therefore ‘skipped out.’ These subjects, however, were included in the analyses with values on the dependence criteria set to zero (that is, structurally missing). A total of 18.8% of the sample (N= 1416) met criteria for DSM-IV AD. The mean age at first drink for those meeting DSM-IV AD criteria was 14.7 (s.d. = 3.2).
