Table 1 Characteristics of participants at baseline
|  | Total (n = 1666) | Boy (n = 860) | Girl (n = 806) |
|---|---|---|---|
Age, mean ± SD | 10.6 ± 2.31 | 10.6 ± 2.33 | 10.6 ± 2.29 |
 Child (< 10 years old) | 524 (31.5%) | 281 (32.7%) | 243 (30.1%) |
 Adolescent (≥ 10 years old) | 1142 (68.5%) | 579 (67.3%) | 563 (69.9%) |
Mother’s education level, n (%) |  |  |  |
 Middle school or below | 157 (9.4%) | 74 (8.6%) | 83 (10.3%) |
 High or vocational school | 327 (19.6%) | 161 (18.7%) | 166 (20.6%) |
 College or university | 1099 (66.0%) | 577 (67.1%) | 522 (64.8%) |
 Master or PhD | 83 (5.0%) | 48 (5.6%) | 35 (4.3%) |
Father’s education level, n (%) |  |  |  |
 Middle school or below | 117 (7.0%) | 62 (7.2%) | 55 (6.8%) |
 High or vocational school | 375 (22.5%) | 178 (20.7%) | 197 (24.4%) |
 College or university | 1022 (61.3%) | 537 (62.4%) | 485 (60.2%) |
 Master or PhD | 152 (9.1%) | 83 (9.7%) | 69 (8.6%) |
Household income, n (%) | Â | Â | Â |
 <100,000 yuan | 183 (11.0%) | 87 (10.1%) | 96 (11.9%) |
 100,000-200,000 yuan | 491 (29.5%) | 252 (29.3%) | 239 (29.7%) |
 200,000-400,000 yuan | 578 (34.7%) | 302 (35.1%) | 276 (34.2%) |
 >400,000 yuan | 277 (16.6%) | 142 (16.5%) | 135 (16.7%) |
 Refuse to answer | 137 (8.2%) | 77 (9.0%) | 60 (7.4%) |