Table 1 Summary metrics for average sleep and light for Regular and Irregular groups.

From: Irregular sleep/wake patterns are associated with poorer academic performance and delayed circadian and sleep/wake timing

Variable Regular Irregular p-value
Sleep duration (h)
Clock Day 0.17 ± 0.14 1.31 ± 0.77 p < 0.0001
Biological Day 1.07 ± 0.95 1.37 ± 0.67 p = 0.12
Clock Night 6.61 ± 0.44 5.01 ± 0.91 p < 0.0002
Biological Night 5.71 ± 1.17 4.96 ± 0.83 p = 0.06
Illuminance (lux)
Clock Day 207 ± 92 128 ± 84 p = 0.03
Biological Day 200 ± 87 104 ± 61 p = 0.01
Clock Night 38 ± 30 39 ± 47 p = 0.79
Biological Night 14 ± 8 54 ± 96 p = 0.15
Normalized illuminance
Clock Day 1.70 ± 0.20 1.55 ± 0.25 p = 0.01
Biological Day 1.63 ± 0.05 1.36 ± 0.30 p = 0.001
Clock Night 0.30 ± 0.20 0.45 ± 0.25 p = 0.09
Biological Night 0.12 ± 0.07 0.50 ± 0.42 p = 0.001
  1. Values for each group are mean ± standard deviation. Clock Day is 10:00 to 22:00, Clock Night is 22:00 to 10:00. Biological Night is salivary dim light melatonin onset (DLMO) to DLMO + 10 h (i.e., 10 h after DLMO). Biological Day is DLMO + 10 h to DLMO. Normalized illuminance is illuminance divided by the individual’s average daily illuminance. A nonparametric statistical test (ranksum) was used to test for differences between groups.