The total sample size from same-sex twin pairs on which we had data for AC (that is, excluding life-time abstainers) and AD, and which were used in these analyses, was 5,073, and consisted of 2,090 complete pairs and 893 twins whose cotwins did not participate. By zygosity, the numbers of complete pairs were monozygotic (MZ) male pairs 770; dizygotic (DZ) male 598; MZ female 440; and DZ female 282.
