In the ALSPAC sample, the measure of alcohol problems (in the past year) was a factor score derived from items assessed in a computer-assisted clinic interview: the 10-item Alcohol Use Disorders Identification Test (AUDIT; Babor et al., 2001), the seven DSM-IV alcohol dependence items (American Psychiatric Association, 2000), and three additional alcohol consequences items, as previously described (Salvatore et al., 2014; Edwards et al., 2015). Values for the alcohol problems factor score ranged from −0.45 to 4.18. In FT12, COGA, and IASPSAD, the measure of alcohol problems was a sum score of lifetime DSM-IV alcohol dependence symptoms (range: 0-7) assessed with a personal interview using the Semi-Structured Assessment for the Genetics of Alcoholism (Bucholz et al., 1994). The mean (SD) numbers of alcohol dependence symptoms for FT12, COGA (all ages/under age 27), and IASPSAD were 1.1 (1.4), 2.2 (2.3)/1.7 (1.8), and 6.4 (1.0), respectively. Across all studies, participants who had not initiated alcohol use at the time of assessment were coded as missing for the AUD measures, and were not included in the genetic analyses or the sample sizes reported above.
