Table 1 Bedtime, sleep duration, and cumulative score for brief sleep questionnaire for Japanese children by sex/grade

Weekday bedtime

boy

21:09

0:38

21:20

0:40

21:27

0:38

21:36

0:39

21:53

0:41

22:06

0:45

< 0.001

girl

21:11

0:38

21:22

0:39

21:26

0:40

21:42

0:41

22:00

0:43

22:10

0:46

< 0.001

Weekend bedtime

boy

21:33

0:48

21:42

0:47

21:54

0:46

22:04

0:49

22:19

0:49

22:30

0:54

< 0.001

girl

21:36

0:46

21:48

0:47

21:53

0:47

22:10

0:52

22:22

0:50

22:36

0:48

< 0.001

Weekday sleep duration, hours

boy

9.3

0.7

9.1

0.7

9.0

0.7

8.8

0.7

8.6

0.7

8.4

0.8

< 0.001

girl

9.3

0.7

9.1

0.7

9.0

0.7

8.8

0.7

8.4

0.7

8.3

0.8

< 0.001

Weekend sleep duration, hours

boy

9.5

0.8

9.3

0.8

9.1

0.8

8.9

0.9

8.9

0.9

8.8

0.9

< 0.001

girl

9.5

0.8

9.5

0.9

9.3

0.8

9.2

0.8

9.1

0.9

9.0

1.0

< 0.001

Cumulative score of the brief sleep questionnaire for Japanese children

boy

24.9

3.2

25.0

3.3

24.4

3.2

24.7

3.5

24.5

3.3

24.4

3.2

< 0.001

girl

25.0

3.3

25.0

3.4

24.9

3.2

24.7

3.2

24.6

3.1

24.6

3.5

< 0.001