Because Wave 4 interviews yielded the largest sample size and covered lifetime psychiatric and psychosocial information in young adulthood, we limited the sample to MOAFTS participants who completed Wave 4 interviews. However, data from baseline, Wave 3, and 5, which were available for over 95% of Wave 4 participants, were integrated into coding ever drinking, timing of first alcohol use and AUD diagnosis; in cases where first alcohol consumption or AUD criteria were endorsed prior to Wave 4, we used the age at onset reported in the interview in which it was first endorsed. The Wave 4 sample consisted of 1,038 monozygotic (MZ) twin pairs, 735 dizygotic (DZ) twin pairs, and 241 twins whose co-twins did not participate.
