The number of participants aged 15–17 who gave two or more positive responses on the CAGE was low (see Table 1). This leads to numerical problems when analyzing longitudinal twin data. Therefore, the analyses were conducted on the dichotomy of zero vs. one or more yes answers. In analyses that are described in more detail below, we investigated whether this dichotomization influenced the results.Table 1Prevalence of reporting 0, 1 or 2+ yes answers on the CAGE by sex and age groupAgeMalesFemalesTotal no. of observations0 (%)1 (%)2+ (%)No. of observations0 (%)1 (%)2+ (%)No. of observations15–17435 (84.1)56 (10.8)26 (5.0)517629 (91.0)45 (6.5)17 (2.5)6911,20818–20956 (68.7)268 (19.3)167 (12.0)1,3911,885 (83.8)244 (10.8)120 (5.3)2,2493,64021–23813 (63.0)295 (22.9)183 (14.2)1,2911,832 (83.2)242 (11.0)129 (5.9)2,2033,49424–26677 (61.8)240 (21.9)178 (16.3)1,0951,629 (83.8)199 (10.2)116 (6.0)1,9443,03927–29585 (67.2)171 (19.7)114 (13.1)8701,393 (82.6)183 (10.9)110 (6.5)1,6862,55630–32498 (69.1)129 (17.9)94 (13.0)7211,262 (83.7)148 (9.8)98 (6.5)1,5082,229
