Table 1.

Subject Characteristics and Bedtime Measures for 144 Participants (55 Boys, 89 Girls) at age 15 and 17

	15 y	17 y	Change (17 y–15 y)	p-value (15 y vs. 17 y)
Characteristics
Age (y)	15.9 ± 0.3	17.7 ± 0.3	1.8 ± 0.1	<.001
Height (cm)	171.7 ± 8.2	173.4 ± 9.0	1.7 ± 2.4	.09
Weight (kg)	64.4 ± 11.3	68.5 ± 12.8	4.0 ± 5.2	.005
Body mass index (kg/m2)	21.8 ± 3.3	22.7 ± 3.8	0.9 ± 1.6	.03
School Night Bedtimes
Self-report (clock time ± min)	23:31 ± 57.1	23:57 ± 59.0	26.2 ± 60.7	<.001
Average by Actigraphy (clock time ± min)	00:19 ± 46.1**	00:55 ± 61.0**	35.2 ± 59.2	<.001
Earliest by Actigraphy (clock time ± min)	23:27 ± 63.3	23:56 ± 62.3	28.8 ± 81.1	<.001
Self-report – Average by Actigraphy (min)	−48.6 ± 54.1	−57.5 ± 67.7	−8.9 ± 80.6	.2
Self-report – Earliest by Actigraphy (min)	4.0 ± 76.7	1.5 ± 72.6	−2.5 ± 106.0	.8
Non-school Night Bedtimes
Self-report (clock time ± min)	01:04 ± 68.2#	01:33 ± 75.5#	28.1 ± 79.9	.001
Average by Actigraphy (clock time ± min)	01:36 ± 69.9**,#	02:26 ± 85.5**,#	50.4 ± 92.9*	<.001
Earliest by Actigraphy (clock time ± min)	00:51 ± 64.0*,#	01:42 ± 89.8#	51.3 ± 94.4*	<.001
Self-report – Average by Actigraphy (min)	−31.4 ± 68.1#	−53.7 ± 94.4	−22.2 ± 113.2	.02
Self-report – Earliest by Actigraphy (min)	13.3 ± 69.1	−9.9 ± 100.4	−23.2 ± 114.0	.02
Night-to-night Bedtime Variability
Actigraphy (min)	65.8 ± 36.2	73.0 ± 30.9	7.2 ± 43.2	.048

^*p < .05

^**p < .01 vs. self-report during the same year.

^#p < .01 vs. school nights during the same year.