Table 3. Regression Coefficients of the Sample Main Effect (Lockdown vs Control) in Models With Different Dependent Variables^a.

Dependent variable	Participants, No.	β (SE)	Corrected P valueb	Uncorrected P valueb	R2β* (95% CI)c
Sleep characteristics
Scheduled days
Bedtime	7268	0.32 (0.04)	<.001	<.001	0.023 (0.017-0.030)
Wake time	7214	1.52 (0.09)	<.001	<.001	0.455 (0.440-0.470)
Sleep duration	7214	1.24 (0.08)	<.001	<.001	0.238 (0.222-0.254)
Free days
Bedtime	7266	−0.14 (0.07)	>.99	.11	0.002 (0.001-0.005)
Wake time	7245	0.05 (0.05)	>.99	.31	0.000 (0.000-0.002)
Sleep duration	7244	0.17 (0.05)	.07	.005	0.004 (0.001-0.007)
Sleep deficitd	7193	−1.07 (0.07)	<.001	<.001	0.122 (0.108-0.136)
Alarm clock usee	7276	−0.69 (0.18)	.001	<.001	0.009 (0.006-0.014)
Difficulties falling asleepf	7276	0.16 (0.03)	<.001	<.001	0.005 (0.002-0.009)
Problems sleeping through the nightf	7276	0.15 (0.02)	<.001	<.001	0.006 (0.003-0.011)
Health-related characteristics
HRQoL	7243	1.47 (0.22)	<.001	<.001	0.007 (0.004-0.012)
Smokingg	294	−1.39 (0.63)	.41	.03	0.018 (0.001-0.059)
Alcohol consumptionh	4562	−0.52 (0.07)	<.001	<.001	0.014 (0.008-0.022)
Caffeine consumptioni	7276	−0.62 (0.08)	<.001	<.001	0.010 (0.006-0.015)
Digital media consumptionf,j	7247	0.38 (0.01)	<.001	<.001	0.103 (0.091-0.117)

Abbreviation: HRQoL, health-related quality of life.

^a In all models, age, primary language, and physical illness were also included as fixed effects and school was included as a random effect. The control sample included students who completed surveys from May to July 2017, and the lockdown sample included students who completed surveys from May to June 2020 during high school closure owing to the first COVID-19 wave in Switzerland.

^b P values were corrected for multiple comparisons using the Bonferroni method. Uncorrected P values were multiplied by 15.

^c Semipartial R² statistic.³²

^d Calculated as free days minus scheduled days.

^e Logistic regression model (alarm clock use: yes vs no) using the lme4 package in R.³¹

^f Square-root transformed.

^g Only students older than 16 years who smoked were included. Smoking was measured as number of cigarettes per day.

^h Only students older than 16 years were included. Measured using a custom scale (eTable 1 in the Supplement) with scores ranging from 1 to 15; higher scores indicate greater alcohol consumption.

ⁱ Measured using a custom scale (eTable 1 in the Supplement) with scores ranging from 1 to 20; higher scores indicate greater caffeine consumption.

^j Measured as hours per day.