| Total (n = 8805) | Males (n = 4276) | Females (n = 4471) |
---|---|---|---|
Age* (mean, SD) | 13.72 (1.08) | 13.79 (1.09) | 13.65 (1.06) |
Gender (% female) | 51.1% | n/a | n/a |
Grade | |||
 7 | 30.7% | 31.4% | 29.6% |
 8 | 33.4% | 33.2% | 33.8% |
 9 | 35.9% | 35.4% | 36.7% |
City/Site | |||
 Beijing | 26.5% | 26.3% | 26.9% |
 Hangzhou | 20.3% | 20.9% | 19.9% |
 Wuhan | 20.4% | 19.9% | 20.4% |
 Urumchi | 32.7% | 32.9% | 32.8% |