Table 1.
Characteristics of the study participants in 1996, 2000, 2004, 2008, 2012 and 2017
| Year | 1996 | 2000 | 2004 | 2008 | 2012 | 2017 |
| No of participants | (n=115 814) | (n=106 297) | (n=102 451) | (n=95 680) | (n=100 050) | (n=64 152) |
| n (%) | n (%) | n (%) | n (%) | n (%) | n (%) | |
| Sex | ||||||
| Boys | 57 116 (49.3) | 54 576 (51.3) | 55 998 (54.7) | 48 525 (50.7) | 51 587 (51.6) | 34 582 (53.9) |
| Girls | 58 698 (50.7) | 51 721 (48.7) | 46 453 (45.3) | 47 155 (49.3) | 48 463 (48.4) | 29 570 (46.1) |
| School grade | ||||||
| Junior high school (12–15 years old) | ||||||
| Grade 7 | 14 369 (12.4) | 15 372 (14.5) | 13 146 (12.8) | 13 302 (13.9) | 13 405 (13.4) | 7384 (11.5) |
| Grade 8 | 14 118 (12.2) | 15 916 (15.0) | 13 079 (12.8) | 13 649 (14.3) | 12 884 (12.9) | 7329 (11.4) |
| Grade 9 | 14 311 (12.4) | 15 958 (15.0) | 13 160 (12.8) | 12 925 (13.5) | 12 205 (12.2) | 7415 (11.6) |
| Unknown | 0 (0.0) | 0 (0.0) | 0 (0.0) | 275 (0.3) | 0 (0.0) | 87 (0.1) |
| Senior high school (15–18 years old) | ||||||
| Grade 10 | 24 696 (21.3) | 21 142 (19.9) | 21 815 (21.3) | 20 157 (21.1) | 21 480 (21.5) | 14 201 (22.1) |
| Grade 11 | 25 416 (21.9) | 19 600 (18.4) | 21 530 (21.0) | 18 328 (19.2) | 20 026 (20.0) | 14 212 (22.2) |
| Grade 12 | 22 904 (19.8) | 18 309 (17.2) | 19 721 (19.2) | 16 785 (17.5) | 20 050 (20.0) | 13 404 (20.9) |
| Unknown | 0 (0.0) | 0 (0.0) | 0 (0.0) | 259 (0.3) | 0 (0.0) | 120 (0.2) |
| Alcohol use/smoking in the past 30 days | ||||||
| Alcohol use | 44 545 (38.7) | 39 497 (37.4) | 30 233 (29.7) | 16 110 (16.9) | 12 034 (12.1) | 3584 (5.6) |
| Smoking | 20 070 (17.9) | 16 237 (15.7) | 9614 (9.5) | 4966 (5.2) | 2851 (2.9) | 1183 (1.8) |