Figure 1.

Distribution of sample adolescents’ high school start times and unadjusted means of sleep onset and sleep offset. N = 383 adolescents, with the following school start time categorical sample sizes: n = 53 before 07:30, n = 96 from 07:30 to 07:59, n = 126 from 08:00 to 08:29 and n = 108 at 08:30 or later; adolescents with more than one most frequently occurring school start time (i.e. bi-modal) were grouped by the category of their first observation. The mean time of sleep onset for adolescents were 22:57, 23:07, 23:21, and 23:32 when school start times were before 07:30, 7:30–7:59, 08:00–08:29, and 08:30 or later, respectively. The mean time of sleep offset for adolescents were 05:51, 06:14, 06:30, and 06:58 when school start times were before 07:30, 07:30–07:59, 08:00–08:29, and 08:30 or later, respectively.