Table 2.

Overall analyses on low academic performance n = 1663

	Low academic	Univariate		Multivariatea
	%	OR (95% CI)	p	OR (95% CI)	p
Sex (girl/boy)	17.4/18.6	0.92 (0.72–1.19)	0.53	1.00 (0.77–1.31)	0.98
Senior grade (4–6)/junior (1–3)	18.4 / 17.6	1.06 (0.82–1.36)	0.65	1.11 (0.84–1.45)	0.47
Wakeup time on week day
< 6:30 a.m.	14.7	1		1
6:30 to < 7:00	20.4	1.49 (1.15–1.93)	< 0.01	1.36 (1.03–1.78)	0.03
≥ 7:00	32.3	2.77 (1.59–4.81)	< 0.001	2.48 (1.36–4.50)	< 0.01
Skipping breakfast (yes/no)	26.4/17.4	1.70 (1.09–2.65)	0.02	1.10 (0.68–1.78)	0.71
Screen time on week day (≥ 2 h/< 2 h)	22.3/15.3	1.59 (1.24–2.05)	< 0.001	1.35 (1.04–1.76)	0.03
Physical activity
Very often	15.6	1		1
Often	18.4	1.22 (0.89–1.66)	0.22	1.30 (0.94–1.79)	0.11
Rarely	19.8	1.34 (0.95–1.88)	0.09	1.33 (0.93–1.90)	0.11
Bedtime on week day (late/not late) late: ≥ 10 for junior, and ≥ 10:30 for senior grades children	20.8/17.5	1.23 (0.87–1.76)	0.24	0.87 (0.59–1.28)	0.49
Daytime sleepiness (yes/no)	21.0/17.4	1.27 (0.92–1.74)	0.15	1.10 (0.78–1.54)	0.58
Obesity (yes/no)	20.3/17.8	1.18 (0.76–1.83)	0.47	1.07 (0.67–1.70)	0.78
Cram school (no/yes)	19.1/14.7	1.37 (1.01–1.86)	0.04	1.01 (0.73–1.40)	0.96
Study duration at home (<1 h/≥ 1 h)	21.5/12.5	1.89 (1.43–2.50)	< 0.001	1.82 (1.34–2.49)	< 0.001
Paternal smoke (yes/no)	22.2/14.7	1.66 (1.29–2.14)	< 0.001	1.47 (1.12–1.92)	< 0.01
Maternal smoke (yes/no)	31.3/16.3	2.34 (1.66–3.29)	< 0.001	1.87 (1.29–2.72)	< 0.001
Subjective SES
High	13.9	1		1
Middle	18.8	1.43 (1.04–1.97)	0.03	1.37 (0.99–1.90)	0.06
Low	20.8	1.62 (1.14–2.32)	< 0.01	1.48 (1.03–2.14)	0.04

SES socioeconomic status, OR odds ratio, CI confidence interval

^aAll variables were simultaneously included in the multivariate model. The numbers in Italics showed a statistical significant