Table 1.
Distributions of verbal ability, alcohol variables and covariates in monozygotic (MZ) and dizygotic (DZ) twins
| Men |
Women |
p value |
||||
|---|---|---|---|---|---|---|
| MZ (n = 107) | DZ (n = 192) | MZ (n = 104) | DZ (n = 191) | Sex difference | Zygosity difference | |
| Age, mean (s.d.) | 26.3 (1.3) | 26.1 (1.4) | 26.2 (1.3) | 26.1 (1.2) | 0.639 | 0.153 |
| WAIS-R: Vocabulary, mean (s.d.) | 51.3 (9.7) | 46.2 (9.9) | 49.8 (10.0) | 48.3 (10.1) | 0.339 | <0.001 |
| Alcohol dependence, n (%) | 48 (44.9) | 102 (53.1) | 44 (42.3) | 74 (38.7) | 0.013 | 0.582 |
| Alcohol dependence symptoms, mean (s.d.) | 2.4 (1.8) | 2.9 (2.0) | 2.3 (1.8) | 2.2 (2.0) | 0.002 | 0.271 |
| Maximum number of drinks, mean (s.d.)a | 22.4 (10.6) | 24.7 (9.8) | 14.3 (7.0) | 14.3 (7.5) | <0.001 | 0.199 |
| RAPI score at 18.5 years, mean (s.d.)b | 29.9 (7.9) | 32.8 (8.6) | 31.5 (8.8) | 31.7 (9.0) | 0.875 | 0.048 |
| Alcohol abuse, n (%) | 4 (3.7) | 1 (0.5) | 0 | 3 (1.6) | 0.488 | 0.389 |
| Drug abuse or dependence, n (%) | 1 (0.9) | 2 (1.0) | 0 | 3 (1.6) | 0.987 | 0.332 |
| Antisocial personality disorder, n (%) | 3 (2.8) | 15 (7.8) | 3 (2.9) | 2 (1.0) | 0.006 | 0.335 |
| Depressive disorder, n (%) | 17 (15.9) | 38 (19.8) | 38 (36.5) | 75 (39.3) | <0.001 | 0.373 |
| Anxiety disorder, n (%) | 2 (1.9) | 12 (6.3) | 19 (18.3) | 15 (7.9) | 0.002 | 0.214 |
| Age at initiation of daily smoking, n (%) | ||||||
| Non-smoker | 53 (49.5) | 70 (36.5) | 54 (51.9) | 89 (46.6) | ||
| >17 years | 20 (18.7) | 39 (20.3) | 19 (18.3) | 34 (17.8) | ||
| 15–17 years | 16 (15.0) | 50 (26.0) | 17 (16.4) | 43 (22.5) | ||
| <15 years | 18 (16.8) | 33 (17.2) | 14 (13.5) | 25 (13.1) | 0.298 | 0.061 |
| Age at initiation of drinking to intoxication, n (%)c | ||||||
| > 17 years or never | 9 (8.4) | 20 (10.4) | 19 (18.5) | 28 (14.7) | ||
| 15–17 years | 57 (53.3) | 97 (50.5) | 48 (46.6) | 87 (45.6) | ||
| <15 years | 41 (38.3) | 75 (39.1) | 36 (35.0) | 76 (39.8) | 0.063 | 0.801 |
| Basic education, n (%)d | ||||||
| High school | 74 (73.3) | 99 (55.9) | 78 (76.5) | 115 (62.5) | ||
| Lower | 27 (26.7) | 78 (44.1) | 24 (23.5) | 69 (37.5) | 0.191 | <0.001 |
WAIS-R, Wechsler Adult Intelligence Scale – Revised; s.d., standard deviation; RAPI, Rutgers Alcohol Problem Index ;
a
Information not available for two DZ men and three DZ women.
b
Information not available for five MZ men, nine DZ men, four MZ women and eight DZ women.
c
Information not available for one MZ woman.
d
Information not available for six MZ men, 15 DZ men, two MZ women and seven DZ women.