Table 1.
Characteristics of samples used in analyses
| Characteristic | Entire sample (N=2,410) | Ever-drinkers before age 18 (N=1,550) |
|---|---|---|
| Ancestry, N (%) | ||
| European | 1,648 (68.4) | 1,130 (72.9) |
| African | 762 (31.6) | 420 (27.1) |
| Sex, N (%) | ||
| Males | 1,182 (49.1) | 784 (50.6) |
| Females | 1,228 (51.0) | 766 (49.4) |
| Age at first interview, years | ||
| Mean ± sd | 16.3 ± 3.2 | 16.7 ± 3.0 |
| Range | 12–22 | 12–22 |
| No. of interviews | ||
| Mean ± sd | 3.2 ± 1.1 | 3.2 ± 1.1 |
| Range | (1–5) | (1–5) |
| Family status, N (%) | ||
| From high-risk families | 2,096 (87.0) | 1,384 (89.3) |
| From comparison families | 314 (13.0) | 166 (10.7) |
| No. of extended families | 781 | 645 |
| No. of nuclear families | ||
| Only full-siblings | 1,629 | 1,151 |
| Including half-siblings | 1,438 | 1,044 |
| No. of individuals per extended family, median (range) | 2 (1–24) | 2 (1–17) |
| Drinking milestones reached before age 18, N (%) | ||
| First drink | 1,573 (65.3) | 1,550 (100.0) |
| First intoxication | 1,170 (48.6) | 1,147 (74.0) |
| First DSM-5 symptom | 702 (29.1) | 683 (44.1) |
| Among those who exhibit a first intoxication before age 18 | ||
| Mean age ± sd | 15.3 (1.5) | 15.4 (1.4) |
| Age range | 8–17 | 12–17 |
| Among those who exhibit a first DSM-5 symptom before age 18 | ||
| Mean age ± sd | 15.6 (1.3) | 15.6 (1.2) |
| Age range | 10–17 | 12–17 |
| rs1229984, N (%) | ||
| GG | 2,270 (94.2) | 1,452 (93.7) |
| GA | 137 (5.7) | 96 (6.2) |
| AA | 3 (0.1) | 2 (0.1) |
| Reported proportion of best friends who use alcohol between ages 12–17, N (%) | ||
| None | 746 (31.0) | 239 (15.4) |
| Few | 981 (40.7) | 708 (45.7) |
| Most | 513 (21.3) | 453 (29.2) |
| All | 170 (7.1) | 150 (9.7) |