Factors | Sleep duration before school days | Non-school day catch-up sleep duration | Total | ||||||
<0 | 0 (Reference) | 0 - 1 | 1 - 2 | >2 hrs. | |||||
Number (%) | ≤7 hrs. | 44 (1.6%) | 217 (8.0%) | 359 (13.2%) | 280 (10.3%) | 304 (11.2%) | 1204 (44.2%) | ||
7 hrs.< | 135 (5.0%) | 495 (18.2%) | 561 (20.6%) | 240 (8.8%) | 87 (3.2%) | 1518 (55.8%) | |||
Grade | ≤7 hrs. | 9.2, 1.8 | 9.4, 1.7 | 9.3, 1.8 | 9.2, 1.8 | 9.4, 1.8 | 9.3, 1.8 | ||
7 hrs.< | 6.9, 1.7 | 6.6, 1.5 | 6.7, 0.7 | 6.7, 1.5 | 7.1**, 2.0 | 6.7, 1.6 | |||
P value | <0.01 | <0.01 | <0.01 | <0.01 | <0.01 | <0.01 | |||
Gender (male = 1, female = 2) | ≤7 hrs. | 1.3, 0.5 | 1.4, 0.5 | 1.5**, 0.5 | 1.5**, 0.5 | 1.6**, 0.5 | 1.5, 0.5 | ||
7 hrs.< | 1.3**, 0.5 | 1.4, 0.5 | 1.5**, 0.5 | 1.6**, 0.5 | 1.6**, 0.5 | 1.5, 0.5 | |||
P value | 0.05< | 0.05< | 0.05< | 0.05< | 0.05< | 0.05< | |||
Bedtime before school days | ≤7 hrs. | 23.8, 1.0 | 23.6, 0.9 | 23.7, 0.9 | 23.9**, 0.9 | 24.2**, 1.0 | 23.9, 0.9 | ||
7 hrs.< | 21.7, 0.9 | 21.8, 0.7 | 22.1**, 0.7 | 22.3**, 0.6 | 22.3**, 0.7 | 22.0, 0.7 | |||
P value | <0.01 | <0.01 | <0.01 | <0.01 | <0.01 | <0.01 | |||
Bedtime before non-school days | ≤7 hrs. | 24.9**, 1.2 | 24.0, 1.1 | 23.9, 1.2 | 24.0, 1.2 | 24.3**, 1.3 | 24.1, 1.2 | ||
7 hrs.< | 22.7**, 1.1 | 22.3, 0.9 | 22.4, 0.9 | 22.5, 0.9 | 22.5, 1.0 | 22.4, 0.9 | |||
P value | <0.01 | <0.01 | <0.01 | <0.01 | <0.01 | <0.01 | |||
Waking time on school days | ≤7 hrs. | 6.1, 0.7 | 6.1, 0.7 | 6.2, 0.8 | 6.4**, 0.7 | 6.3**, 0.7 | 6.3, 0.7 | ||
7 hrs.< | 6.7*, 0.7 | 6.5, 0.5 | 6.5, 0.5 | 6.6, 0.5 | 6.6, 0.6 | 6.6, 0.5 | |||
P value | <0.01 | <0.01 | <0.01 | <0.01 | <0.01 | <0.01 | |||
Waking time on non-school days | ≤7 hrs. | 6.1, 0.8 | 6.5, 1.0 | 7.4**, 1.1 | 8.5**, 1.1 | 9.9**, 1.3 | 8.1, 1.7 | ||
7 hrs.< | 6.4**, 0.9 | 7.0, 0.8 | 7.8**, 0.8 | 8.7**, 0.8 | 10.0**, 1.1 | 7.7, 1.2 | |||
P value | <0.05 | <0.01 | <0.01 | <0.01 | 0.05< | <0.01 | |||
Sleep duration before non-school days (hrs.) | ≤7 hrs. | 5.2**, 1.0 | 6.5, 0.7 | 7.5**, 0.7 | 8.5**, 0.7 | 9.6**, 1.1 | 8.0, 1.5 | ||
7 hrs.< | 7.7**, 0.8 | 8.7, 0.6 | 9.4**, 0.5 | 10.3**, 0.5 | 11.5**, 0.7 | 9.3, 1.1 | |||
P value | <0.01 | <0.01 | <0.01 | <0.01 | <0.01 | <0.01 | |||
Averaged sleep duration a day (hrs.) | ≤7 hrs. | 6.0**, 0.8 | 6.5, 0.7 | 6.8**, 0.7 | 7.1**, 0.7 | 7.1**, 0.8 | 6.9, 0.8 | ||
7 hrs.< | 8.6, 0.8 | 8.7, 0.6 | 8.7, 0.6 | 8.8**, 0.5 | 9.2**, 0.5 | 8.8, 0.6 | |||
P value | <0.01 | <0.01 | <0.01 | <0.01 | <0.01 | <0.01 | |||
Social jetlag (hrs.) | ≤7 hrs. | 0.6, 0.6 | 0.4, 0.7 | 0.7**, 0.7 | 1.1**, 0.7 | 1.8**, 0.8 | 1.0, 0.9 | ||
7 hrs.< | 0.3, 0.9 | 0.5, 0.6 | 0.8**, 0.6 | 1.2**, 0.6 | 1.8**, 0.7 | 0.8, 0.7 | |||
P value | 0.05< | p<0.05 | 0.05< | 0.05< | 0.05< | <0.01 | |||
Self-reported academic performance (1, very good, …, 4, poor) | ≤7 hrs. | 2.7, 0.9 | 2.6, 0.8 | 2.5, 0.8 | 2.6, 0.9 | 2.6, 0.8 | 2.6, 0.8 | ||
7 hrs.< | 2.4, 0.8 | 2.3, 0.8 | 2.3, 0.8 | 2.3, 0.7 | 2.6**, 0.8 | 2.3, 0.8 | |||
P value | NS | <0.01 | <0.01 | <0.01 | 0.05< | <0.01 | |||
Standardized BMI | ≤7 hrs. | 0.3, 1.4 | 0.1, 1.0 | 0.0, 0.9 | 0.0, 1.0 | 0.0, 1.0 | 0.0, 1.0 | ||
7 hrs.< | 0.0, 1.1 | 0.0, 1.0 | −0.1, 1.0 | −0.1, 0.9 | −0.1, 1.1 | 0.0, 1.0 | |||
P value | 0.05< | 0.05< | 0.05< | 0.05< | 0.05< | 0.05< | |||
Sleepiness during class (1, never, …, 4, always) | ≤7 hrs. | 2.5, 0.9 | 2.3, 0.9 | 2.3, 0.8 | 2.2, 0.9 | 2.4, 0.9 | 2.3, 0.9 | ||
7 hrs.< | 1.8, 0.7 | 1.7, 0.7 | 1.7, 0.7 | 1.8, 0.6 | 2.0**, 0.7 | 1.7, 0.7 | |||
P value | <0.01 | <0.01 | <0.01 | <0.01 | <0.01 | <0.01 | |||
After-school activity (hrs./week) | ≤7 hrs. | 9.5, 10.2 | 7.9, 10.1 | 8.3, 9.1 | 7.2, 8.0 | 6.6, 8.1 | 7.6, 8.9 | ||
7 hrs.< | 6.6*, 6.6 | 5.1, 6.3 | 4.2, 5.0 | 3.7**, 4.9 | 4.4, 5.9 | 4.6, 5.7 | |||
P value | 0.05< | <0.01 | <0.01 | <0.01 | <0.01 | <0.01 | |||
Physical activity (days/week) | ≤7 hrs. | 4.5, 2.7 | 4.3, 3.0 | 3.5**, 3.1 | 2.9**, 3.0 | 2.0**, 2.7 | 3.2, 3.1 | ||
7 hrs.< | 4.1*, 2.6 | 3.4, 2.7 | 2.9, 2.7 | 2.5**, 2.7 | 2.7, 2.8 | 3.1, 2.7 | |||
P value | 0.05< | <0.01 | <0.01 | 0.05< | <0.05 | 0.05< | |||
Breakfast taking (1, always, …, 4, never) | ≤7 hrs. | 1.6, 0.8 | 1.3, 0.7 | 1.2, 0.6 | 1.3, 0.6 | 1.4, 0.7 | 1.3, 0.7 | ||
7 hrs.< | 1.2, 0.5 | 1.1, 0.4 | 1.1, 0.4 | 1.1, 0.5 | 1.3**, 0.7 | 1.1, 0.4 | |||
P value | <0.01 | <0.01 | <0.01 | <0.05 | 0.05< | <0.01 | |||
Defecation frequency (1. every day,….4, twice a week or less) | ≤7 hrs. | 1.7, 1.0 | 1.5, 0.8 | 1.6, 0.9 | 1.7, 0.9 | 1.7, 0.9 | 1.7, 0.9 | ||
7 hrs.< | 1.6, 0.8 | 1.6, 0.8 | 1.6, 0.9 | 1.6, 0.8 | 2.0**, 1.0 | 1.6, 0.9 | |||
P value | 0.05< | 0.05< | 0.05< | 0.05< | <0.05 | 0.05< | |||
Averaged screen time a day (hrs.) | ≤7 hrs. | 4.1**, 2.5 | 2.9, 1.9 | 2.9, 1.9 | 3.1, 1.7 | 3.6**, 2.0 | 3.2, 1.9 | ||
7 hrs.< | 2.4, 1.5 | 2.2, 1.9 | 2.5**, 1.5 | 2.6**, 1.5 | 2.9**, 1.7 | 2.5, 1.5 | |||
P value | <0.01 | <0.01 | <0.01 | <0.01 | <0.01 | <0.01 | |||