Characteristics of the study sample split by risk factor*
| Risk factor | n | Sex, % male | Age, mean ± SD, yr | Parents’ education, mean ± SD, yr | Location, % Amsterdam | Smoking, % exposed | Alcohol, % exposed | DRD4, % 7R carrier | DAT1, % 10/6 homozygote |
|---|---|---|---|---|---|---|---|---|---|
| Full sample | 239 | 53.6 | 17.1 ± 3.0 | 12.1 ± 2.4 | 49.0 | 22.2 | 18.8 | 36.0 | 14.2 |
| Exposed to smoking | |||||||||
| Yes | 53 | 50.9 | 18.1 ± 3.0 | 11.5 ± 2.3 | 50.9 | — | 22.6 | 39.6 | 11.3 |
| No | 186 | 54.3 | 16.9 ± 3.0 | 12.2 ± 2.4 | 48.4 | — | 17.7 | 34.9 | 15.1 |
| p value | 0.78 | 0.010 | 0.07 | 0.86 | — | 0.54 | 0.64 | 0.64 | |
| Exposed to alcohol | |||||||||
| Yes | 45 | 57.8 | 17.9 ± 2.7 | 12.7 ± 2.5 | 37.8 | 22.4 | — | 26.7 | 15.6 |
| No | 194 | 52.6 | 17.0 ± 3.1 | 11.9 ± 2.4 | 51.5 | 21.1 | — | 38.1 | 13.9 |
| p value | 0.64 | 0.05 | 0.040 | 0.13 | 0.54 | — | 0.20 | 0.96 | |
| DRD4 7R carrier | |||||||||
| Yes | 86 | 53.5 | 17.1 ± 3.1 | 12.3 ± 2.7 | 52.3 | 24.4 | 14.0 | — | 11.6 |
| No | 153 | 53.6 | 17.2 ± 3.0 | 11.9 ± 2.2 | 47.1 | 20.9 | 21.6 | — | 15.7 |
| p value | 0.99 | 0.84 | 0.19 | 0.52 | 0.64 | 0.20 | — | 0.50 | |
| DAT1 10/6 homozygote | |||||||||
| Yes | 34 | 64.7 | 16.8 ± 2.4 | 11.7 ± 2.2 | 41.2 | 17.6 | 20.6 | 29.4 | — |
| No | 205 | 51.7 | 17.2 ± 3.1 | 12.1 ± 2.5 | 50.2 | 22.9 | 18.5 | 37.1 | — |
| p value | 0.22 | 0.53 | 0.30 | 0.43 | 0.64 | 0.96 | 0.50 | — | |
SD = standard deviation.
↵* We analyzed the data with Pearson χ2 tests for categorical variables and with 1-way analysis of variance for continuous variables.