Table 1 Demographic data and sleep habits in university students in Japan and China
|  | Japanese (n = 447) | Chinese (n = 327) |  |
|---|---|---|---|
Mean age (years) | 21.5 (1.6) | 23.3 (2.7) | ** |
Sex, %male | 62.8 | 53.4 | ** |
Sleep habits (school days) | |||
  Bedtime | 01:09 (1:01) | 23:58 (0:43) | *** |
 Sleep latency (min) | 15.1 (11.3) | 16.1 (11.7) | n.s. |
 Sleep onset time | 01:24 (1:02) | 00:15 (0:46) | *** |
 Wake time | 08:01 (1:11) | 07:42 (0:49) | *** |
 Midpoint of sleep | 04:43 (0:57) | 3:58 (0:39) | *** |
 Sleep period time (h) | 6.62 (1.13) | 7.46 (0.90) | *** |
Sleep habits (free days) | |||
  Bedtime | 01:37 (1:12) | 00:22 (0:51) | *** |
 Sleep latency (min) | 16.0 (13.0) | 14.9 (11.7) | n.s. |
 Sleep onset time | 01:52 (1:14) | 00:38 (0:52) | *** |
 Wake time | 09:35 (1:25) | 08:46 (1:01) | *** |
 Midpoint of sleep | 05:45 (1:11) | 4:42 (0:49) | *** |
 Sleep period time (h) | 7.70 (1.25) | 8.15 (0.95) | *** |
Social jet lag (h) | 1.04 (0.82) | 0.73 (0.56) | *** |