Demographics and background variables of 86 270 study participants
| Age, mean (SD) | 15.3 (0.6) |
| Boys, n (%) | 42 531 (49.3) |
| Student in year 8, n (%) | 43 998 (51.0) |
| Maternal education,* n (%) | |
| Comprehensive | 3713 (4.7) |
| Upper secondary | 21 651 (27.3) |
| Additional studies | 18 107 (22.8) |
| University | 35 796 (45.2) |
| Parental relations: talks about concerns,† n (%) | |
| Hardly ever | 5362 (6.5) |
| Occasionally | 17 894 (21.5) |
| Fairly often | 21 041 (25.3) |
| Often | 38 782 (46.7) |
*Data on maternal education were available for 79 267 participants (91.9% of total).
†Data on parental relations were available for 83 079 participants (96.3%).
SD, standard deviation.