Table 2.
Change in sleep indices for DOZE (Delivering Online Zzz’s with Empirical Support) study finishersa.
| Sleep diary variable | Period 1, mean (SD) | Period 2, mean (SD) | t testb (df) | P value | Cohen d |
| Bedtime variability (hours) | 4.26 (2.16) | 4.96 (4.08) | 0.52 (49) | .60 | 0.07 |
| Sleep attempt variability (hours) | 4.04 (2.19) | 4.01 (2.13) | 0.88 (49) | .38 | 0.12 |
| Wake time variability (hours) | 4.59 (2.47) | 4.62 (2.38) | −0.22 (49) | .83 | 0.03 |
| Rise time variability (hours) | 4.71 (2.41) | 5.05 (2.83) | −0.13 (49) | .90 | 0.02 |
| Nap duration (hours) | 0.370 (0.50) | 0.220 (0.32) | 1.63 (32) | .11 | 0.28 |
| Morning lingering in bed (hours) | 0.402 (0.28) | 0.353 (0.30) | 2.24 (46) | .03 | 0.30 |
| Time in bed (hours) | 8.35 (1.06) | 8.49 (0.85) | −2.40 (49) | .02 | 0.34 |
| Total sleep time (hours) | 7.34 (0.93) | 7.67 (0.97) | −4.23 (49) | <.001 | 0.60 |
| Total wake time (hours) | 1.00 (0.54) | 0.837 (0.55) | 2.54 (47) | .01 | 0.36 |
| Sleep efficiency (%) | 87.67 (6.44) | 90.18 (6.46) | −3.43 (49) | .001 | 0.48 |
| Frequency of sleep-interfering substance usec | 0.142 (0.21) | 0.131 (0.21) | 0.34 (49)d | .74 | 0.05 |
aTest statistic and Cohen d are for log-transformed variables, whereas means and SDs refer to untransformed variables.
bTest is 2-tailed.
cFrequency of substance use refers to the proportion of days within a period in which sleep-interfering substance use was endorsed in the sleep diary.
dNot log-transformed.