Table 1.
Demographic information of participants [n (%)].
| Variables | Total | Male | Female |
|---|---|---|---|
| Province | |||
| Jiangsu | 3,735 (17.8) | 1,786 (17.2) | 1,949 (18.5) |
| Guangdong | 4,480 (21.4) | 2,354 (22.6) | 2,126 (20.1) |
| Yunnan | 4,260 (20.3) | 1,717 (16.5) | 2,543 (24.1) |
| Gansu | 3,875 (18.5) | 2,016 (19.4) | 1,859 (17.6) |
| Hubei | 4,601 (22.0) | 2,523 (24.3) | 2,078 (19.7) |
| Residence | |||
| Urban | 10,896 (52.0) | 5,829 (56.1) | 5,067 (48.0) |
| Rural | 10,055 (48.0) | 4,567 (43.9) | 5,448 (52.0) |
| Grade | |||
| 7–9 | 10,526 (50.2) | 5,428 (52.2) | 5,098 (48.3) |
| 10–12 | 10,425 (49.8) | 4,968 (47.8) | 5,457 (51.7) |
| Age (year) | |||
| 12 | 2,230 (10.6) | 1,167 (11.2) | 1,063 (10.1) |
| 13 | 4,135 (19.7) | 2,085 (20.1) | 2,050 (19.4) |
| 14 | 3,488 (16.6) | 1,828 (17.6) | 1,660 (15.7) |
| 15 | 2,923 (14.0) | 1,457 (14.0) | 1,466 (13.9) |
| 16 | 4,031 (19.2) | 1,896 (18.2) | 2,135 (20.2) |
| 17 | 2,956 (14.1) | 1,419 (13.6) | 1,537 (14.6) |
| 18 | 1,188 (5.7) | 544 (5.2) | 644 (6.1) |
| Total | 20,951 (100.0) | 10,396 (49.6) | 10,555 (50.4) |