| First data collection | Second data collection | ||||
| VLBW | ELBW | Z | VLBW | ELBW | Z |
Sleep onset time, PM | 22:06 (21:13 - 22:45) | 21:09 (20:28 - 21:59) | 2.61** | 21:41 (20:33 - 22:13) | 21:33 (21:23 - 22:23) | −0.63 |
Sleep offset time, AM | 6:21 (5:39 - 7:13) | 7:05 (6:19 - 4:40) | 2.02* | 6:57 (6:09 - 7:10) | 6:11 (5:53 - 7:06) | −0.98 |
Nocturnal sleep duration (min) | 394.0 (371 - 431) | 436.5 (379 - 475) | −1.52 | 554.0 (512 - 580) | 488.0 (448 - 565) | −0.08 |
Sleep efficiency (%) | 81.2 (76.3 - 86.1) | 74.4 (69.2 - 83.1) | 2.10* | 97.2 (95.3 - 98.6) | 97.0 (93.9 - 98.7) | −0.21 |
WASO (%) | 99.0 (73.0 - 115.0) | 146.5 (94.8 ? 171.3) | 2.89** | 16.0 (8.0 - 27.0) | 15.0 (6.0 - 32.5) | 0.00 |
Number of night-waking | 6.0 (4.5 - 8.0) | 8.5 (7.0 - 10.3) | 2.47** | 0.0 (0.0 - 1.0) | 1.0 (0.0 - 2.5) | −0.62 |
Longest wake episode (min) | 23.0 (19.5 - 27.5) | 36.5 (21.0 - 42.3) | 2.05* | 4.0 (3.0 - 7.0) | 5.0 (2.0 - 10.0) | −0.31 |
Longest sleep episode (min) | 100.0 (66.0 - 133.0) | 92.5 (64.0 - 124.5) | −0.47 | 166.0 (108.0 - 222.0) | 181.0 (125.5 - 198.5) | −0.10 |
Mean activity score (count/min) | 20.3 (15.7 - 24.9) | 23.4 (17.7 - 30.4) | −1.47 | 9.7 (8.9 - 12.0) | 10.3 (8.8 - 13.1) | −0.04 |
ACTX (%) | 63.0 (56.5 - 69.0) | 56.5 (46.5 - 58.3) | 2.75** | 41.4 (34.7 - 43.4) | 38.9 (33.1 - 42.6) | −0.56 |