Table 1.

Sample Demographics and Descriptive Statistics Without Weights by School Start Time

	Overall sample (N=973)	Early school start time (N=343)	Late school start time (N=630)
Demographics/Covariates
Grade 8	458 (47%)	168 (49%)	290 (46%)
Age
12	22 (2%)	6 (2%)	16 (2%)
13	466 (48%)	151 (44%)	315 (50%)
14	436 (45%)	165 (48%)	271 (43%)
15	49 (5%)	21 (6%)	28 (4%)
Female	501 (51%)	158 (46%)	343 (54%)
Race and Hispanic Origin
White	604 (62%)	238 (69%)	366 (58%)
Black	41 (4%)	16 (5%)	25 (4%)
Hispanic	71 (7%)	27 (8%)	44 (7%)
Asian	138 (14%)	31 (9%)	107 (17%)
Two or more races or other	119 (12%)	31 (9%)	88 (14%)
English is home language	915 (94%)	326 (95%)	586 (93%)
Two, married parents at home	837 (86%)	295 (86%)	542 (86%)
Highest level or parent education
Below Bachelor’s	95 (10%)	32 (9%)	63 (10%)
Bachelor’s degree	269 (28%)	99 (29%)	170 (27%)
Master’s degree	431 (44%)	154 (45%)	277 (44%)
Above Master’s	178 (18%)	58 (17%)	120 (19%)
Free and Reduced Priced Meals	53 (5%)	21 (6%)	32 (5%)
Outcomes
School-night sleep duration (hours)
Mean (SD)	8.30 (1.06)	8.15 (0.98)	8.39 (1.09)
Range	2.5–12.0	3.50–11.0	2.5–12.0
School-night bedtime
Mean (SD)	9:54p.m. (1:02)	9:43p.m. (0:57)	10:02p.m. (1:01)
Range	7:00p.m. – 3:00a.m.	7:00p.m. – 3:00a.m.	7:00p.m. – 2:15a.m.
School-day wake time
Mean (SD)	6:12a.m. (0:30)	5:51a.m. (0:25)	6:24a.m. (0:31)
Range	3:00a.m. – 7:45a.m.	3:30a.m. – 7:00a.m.	3:00a.m. – 7:45a.m.
Weekend sleep duration (hours)
Mean (SD)	10.10 (1.47)	10.09 (1.45)	10.11 (1.49)
Range	4.0–17.5	4.0–15.75	4.50–17.50
Sleepiness scale
Mean (SD)	0.22 (0.28)	0.24 (0.28)	0.22 (0.28)
Range	0–2	0–1.3	0–2
Wide awake (0 on sleepiness scale)
Mean (SD)	0.40 (.49)	0.34 (0.48)	0.43 (0.50)
Range	0–1	0–1	0–1

NOTE: Descriptive statistics are based on one of 20 multiply imputed datasets.