Table 1.
Sample characteristics (N = 28,398)
| Variables | n | % |
|---|---|---|
| Sex (female) | 13,417 | 47.2 |
| Grade [age, years] | ||
| Grade 5 [11.1 ± 0.6] | 10,545 | 37.1 |
| Grade 6 [12.1 ± 0.6] | 5,991 | 21.1 |
| Grade 7 [13.0 ± 0.6] | 7,030 | 24.8 |
| Grade 8 [14.0 ± 0.6] | 4,832 | 17.0 |
| School types (private school) | 14,461 | 50.9 |
| Boarding at School (yes) | 2,317 | 8.2 |
| Number of siblings (one) | 5,638 | 19.9 |
| Parental marital status (poor a) | 1,351 | 4.8 |
| Family income (monthly) | ||
| < ¥ 12,000 | 12,506 | 44.0 |
| ¥ 12,000- ¥ 30,000 | 7,423 | 26.1 |
| > ¥ 30,000 | 2,342 | 8.2 |
| Unknown | 6,127 | 21.6 |
| Chronic somatic diseases (yes) | 984 | 3.5 |
| Family history of mental illness (yes) | 267 | 0.9 |
| Anxiety and depressive symptoms (yes) | 2,203 | 7.8 |
| Reduced homework (yes) | 22,901 | 80.6 |
| More extracurricular activities (yes) | 20,137 | 70.9 |
| Increased physical activity (yes) | 22,483 | 79.2 |
| More family time (yes) | 18,366 | 64.7 |
| Reduced academic pressure (yes) | 13,129 | 46.2 |
| Insomnia symptoms at T1 (yes) | 2,802 | 9.9 |
| Insomnia symptoms at T2 (yes) | 2,609 | 9.2 |
a Poor parental marital status included separated, divorced, and widowed