School day

sleep duration

Variables

Regression coefficient

β

P

95% CI

More than 7 hours

Constant

−0.06

−0.42

to

0.30

−0.06

0.746

Grade

0.02

−0.02

to

0.05

0.02

0.396

Gender (male: 1; female: 2)

0.33

0.22

to

0.45

0.15

<0.001

Standardized BMI

−0.06

−0.11

to

−0.01

−0.05

0.030

Self-reported academic performance

0.00

−0.07

to

0.07

0.00

0.952

Sleepiness during class

0.06

−0.02

to

0.14

0.04

0.171

Breakfast taking

0.09

−0.03

to

0.22

0.04

0.143

Defecation frequency

0.00

−0.06

to

0.06

0.00

0.971

After-school activity (hrs./week)

−0.02

−0.03

to

−0.01

−0.09

<0.001

Physical activity (days/week)

−0.03

−0.05

to

−0.01

−0.09

0.001

Average screen time a day (hrs)

0.11

0.04

to

0.19

0.08

0.004

7 hours or less

Constant

1.58

0.97

to

2.19

1.58

<0.001

Grade

0.00

−0.04

to

0.05

0.00

0.883

Gender (male: 1; female: 2)

0.15

−0.01

to

0.32

0.05

0.064

Standardized BMI

−0.03

−0.10

to

0.05

−0.02

0.492

Self-reported academic performance

0.05

−0.05

to

0.14

0.03

0.348

Sleepiness during class

0.04

−0.06

to

0.14

0.02

0.409

Breakfast taking

−0.03

−0.15

to

0.09

−0.01

0.641

Defecation frequency

−0.05

−0.13

to

0.04

−0.03

0.308

After-school activity (hrs./week)

−0.01

−0.02

to

0.00

−0.07

0.012

Physical activity (days/week)

−0.12

−0.14

to

−0.09

−0.26

<0.001

Average screen time a day (hrs)

0.06

−0.03

to

0.14

0.04

0.192