Baseline characteristics of students who completed both baseline and follow-up examinations (n=355)
| Baseline characteristics | Mean±SD |
| Age at baseline (years) | 11.60±0.36 |
| Sex, female, n (%) | 166 (46.8%) |
| Time spent in self-study, more than 2 h/day n (%) | 112 (31.5%) |
| Attending extra-class, yes n (%) | 322 (90.7%) |
| Studying on computer, yes n (%) | 149 (42.0%) |
| Daily time reading printed material indoors (h/d) | 1.16±0.73 |
| Daily time playing video game indoors (h/d) | 1.38±0.67 |
| Daily time watching TV indoors (h/d) | 1.47±0.66 |
| Daily time playing sports indoors (h/d) | 0.48±0.72 |
| Daily time playing/walking outdoors (h/d) | 1.31±0.71 |
| Daily time playing sports outdoors (h/d) | 1.02±0.81 |
SD, standard deviation.