The sample for the current study consists of 5,382 twins (2,691 pairs), representing all twin pairs in which both twins endorsed consumption of at least one alcoholic drink over their lifetimes (97.5% of all complete pairs). Breakdown by sex and zygosity are as follows: 681 female monozygotic (MZ), 480 MZ male, 502 dizygotic (DZ) female, 387 DZ male, and 641 DZ opposite sex twin pairs. Mean age at the time of interview was 29.9 years.
