Table 2. Adjusted Difference-in-Differences Analysis of Changes in Sleep Duration and Timing Among High School Students Before and After a 50- and 65-Minute Delay in School Start Timesa.
| Variable | Delayed-start schools | Comparison schools | Difference-in-differences analysis | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Baseline (n = 122) | Follow-up 1 (n = 141) | Follow-up 2 (n = 90) | Baseline (n = 160) | Follow-up 1 (n = 162) | Follow-up 2 (n = 94) | Baseline to follow-up 1, min | P Value | Baseline to follow-up 2, min | P Value | |
| School night sleep onset timeb | 22:28 (22:14 to 22:41) pm | 22:55 (22:44 to 23:06) pm | 23:09 (22:57 to 23:20) pm | 22:15 (22:06 to 22:25) pm | 22:41 (22:30 to 22:52) pm | 22:41 (22:26 to 22:55) pm | 2 (−13 to 16) | .82 | 16 (−1 to 33) | .06 |
| School night wake-up timec | 6:06 (5:54 to 6:17) am | 7:01 (6:50 to 7:12) am | 7:16 (7:04 to 7:27) am | 6:14 (6:04 to 6:24) am | 6:28 (6:19 to 6:38) am | 6:26 (6:15 to 6:38) am | 41 (32 to 51) | <.001 | 58 (46 to 69) | <.001 |
| School night sleep duration, h:minc | 7:38 (7:24 to 7:52) | 8:05 (7:53 to 8:17) | 8:05 (7:51 to 8:19) | 7:59 (7:47 to 8:10) | 7:45 (7:33 to 7:56) | 7:42 (7:27 to 7:57) | 41 (25 to 57) | <.001 | 43 (25 to 61) | <.001 |
| Weekend night sleep onset timeb | 23:24 (23:02 to 23:45) pm | 23:50 (23:33 pm to 0:07 am) pm | 0:13 (23:54 pm to 0:31 am) am | 23:39 (23:25 to 23:53) pm | 0:08 (23:51 pm to 0:25 am) am | 23:50 (23:27 pm to 0:14 am) pm | −2 (−27 to 23) | .87 | 38 (10 to 67) | .009 |
| Weekend night wake-up timec | 8:51 (8:33 to 9:09) am | 9:05 (8:49 to 9:20) am | 9:17 (9:00 to 9:35) am | 8:44 (8:30 to 8:58) am | 9:25 (9:10 to 9:40) am | 9:06 (8:45 to 9:26) am | −27 (−53 to −1) | .04 | 5 (−24 to 34) | .75 |
| Weekend night sleep duration, h:minc | 9:23 (9:04 to 9:52) | 9:11 (8:54 to 9:27) | 9:00 (8:40 to 9:20) | 9:07 (8:52 to 9:22) | 9:19 (9:03 to 9:35) | 9:18 (8:55 to 9:40) | −24 (−51 to 2) | .07 | −34 (−65 to −3) | .03 |
a
Data are from the START study, spring 2016 through spring 2018. Baseline occurred in spring 2016 (9th grade); follow-up 1, spring 2017 (10th grade); and follow-up 2, spring 2018 (11th grade). Unless otherwise indicated, data are expressed as mean (95% CI).
b
Linear mixed-effects models adjusted for demographic factors and length of daylight, with school fixed effect in place of school random effect.
c
Linear mixed-effects models adjusted for biological sex, socioeconomic status (free or reduced lunch eligibility and parent educational attainment), race and ethnicity, and length of daylight at actigraphy, school- and student-level random effects.