Baseline characteristics of children and parents
| Variable | Value (N=6724) |
| Child sex, n (%) | |
| Boys | 3500 (52.1) |
| Girls | 3224 (48.0) |
| Residence, n (%) | |
| Urban | 2739 (40.8) |
| Rural | 3985 (59.2) |
| Baseline age (years), mean (SD） | 5.7 (4.0） |
| Paternal education level, n (%) | |
| Primary school or less | 2272 (33.8) |
| Junior high school | 2819 (41.9) |
| Senior high school | 1000 (14.9) |
| Junior college or higher | 633 (9.4) |
| Maternal education level, n (%) | |
| Primary school or less | 2978 (44.3) |
| Junior high school | 2440 (36.3) |
| Senior high school | 764 (11.4) |
| Junior college or higher | 542 (8.1) |
| Average household income (¥), median (IQR), mean | |
| 2010 | 4662 (2583, 8433), 7280 |
| 2012 | 6667 (3075, 11 400), 8995 |
| 2014 | 7900 (3986, 13 333), 10 520 |
| 2016 | 8220 (3990, 14 690), 11 971 |
| Birth weight (kg), mean (SD) | 3.2 (0.54） |
IQR, interquartile range.