Table 7 Relationships between baseline usual bedtime and potential variables.

Residency area

Sub-urban

3657

75.86%

1164

24.14%

1 (Reference)

Urban

688

56.77%

524

43.23%

2.39

p < 0.001

Age (years)

6

1432

74.31%

495

25.69%

1 (Reference)

7

2114

70.96%

865

29.04%

1.18 (1.04, 1.35)

p = 0.01

8

799

70.90%

328

29.10%

1.19 (1.01, 1.40)

p = 0.04

Gender

Male

2311

72.17%

891

27.83%

1 (Reference)

Female

2034

71.87%

796

28.13%

1.02 (0.91, 1.14)

p = 0.80

Myopic parent

0

1927

75.99%

609

24.01%

1 (Reference)

1

1428

69.90%

615

30.10%

1.36 (1.20, 1.56)

p < 0.001

2

769

66.46%

388

33.54%

1.60 (1.37, 1.86)

p < 0.001

Parent education

Lower than undergrad

2823

76.36%

874

23.64%

1 (Reference)

Undergrad

1322

65.77%

688

34.23%

1.68 (1.49, 1.89)

p < 0.001

Postgrad

140

56.22%

109

43.78%

2.51 (1.94, 3.27)

p < 0.001

Usual wake-up time

Sleep duration (hours)

Before 6:30 a.m.

1657

89.62%

192

10.38%

1 (Reference)

6:30 to 6:59 a.m.

1862

71.70%

735

28.30%

3.41 (2.87, 4.05)

p < 0.001

7 a.m. and after

826

52.05%

761

47.95%

7.95 (6.65, 9.51)

p < 0.001

< 9.5

1215

48.76%

1277

51.24%

1 (Reference)

≥ 9.5 and < 10

1587

80.27%

390

19.73%

0.23 (0.20, 0.27)

p < 0.001

≥ 10 h

1543

98.66%

21

1.34%

0.01 (0.01, 0.02)

p < 0.001

Reading time weekly total

15.93 ± 6.79

17.14 ± 7.24

1.03 (1.02, 1.03)

p < 0.001

Screen time weekly total

6.70 ± 3.80

6.94 ± 4.02

1.02 (1.00, 1.03)

p = 0.03

Outdoor time weekly total

7.32 ± 3.85

6.97 ± 3.87

0.98 (0.96, 0.99)

p = 0.002