Second, our sample likely contained heavy-drinking individuals never registered for AUD. To explore how much this might bias our results, we examined alcohol consumption at ages 18 to 20 years available from 2 years of military conscription records (1969–1970) in male-male sibling pairs discordant for lifetime AUD registration.33 Standardized alcohol consumption scores for those who did and did not have a subsequent AUD registration were +0.40 and −0.04, respectively. The unaffected sibling from discordant pairs had a mean consumption score of +0.01, suggesting only modestly increased drinking at least in late adolescence. Nonetheless, some of the familial confounding observed in our study could arise because nonregistered close relatives of AUD probands drink at higher rates than the general population.
