Demographic characteristics of participants
| Characteristics | N (%) |
|---|---|
| City/county | |
| Changsha | 1066 (22.6) |
| Shaoyang | 1268 (26.8) |
| Liuyang | 1226 (25.9) |
| Ningxiang | 1167 (24.7) |
| Gender | |
| Male | 2408 (50.9) |
| Female | 2319 (49.1) |
| Age (years) | |
| 11–14 | 2057 (43.5) |
| 15–19 | 2670 (56.5) |
| Grade | |
| 7th–9th | 2459 (52.0) |
| 10th–12th | 2268 (48.0) |
| Ethnic group | |
| Han | 4649 (98.3) |
| Minority | 78 (1.7) |
| Parent's marriage status | |
| Married | 3873 (81.9) |
| Divorced/separated/widowed | 212 (4.5) |
| Declined/missing | 642 (13.6) |
| Father's education level | |
| Primary school | 286 (6.1) |
| Junior School | 1445 (30.6) |
| High School | 1186 (25.1) |
| College and above | 1123 (23.7) |
| Declined/missing | 687 (14.5) |
| Mother's education level | |
| Primary school | 414 (8.8) |
| Junior School | 1673 (35.4) |
| High School | 1194 (25.3) |
| College and above | 776 (16.4) |
| Declined/missing | 670 (14.2) |