Table 1. Sample characteristics.
| Socio-demographic | Categories | Participants | Smoking, drinking and sleep condition | Categories | Participants |
|---|---|---|---|---|---|
| Age (Median ± SD) | – | 18.9 ± 2.3 | Smoking (n, %) | No | 2,100 (98.0%) |
| BMI (Median ± SD) | – | 21.9 ± 4.0 | Yes | 42 (2.0%) | |
| Gender (n, %) | Male | 593 (27.7%) | If smoking, the number of cigarettes smoked per day (Median ± SD) | – | 6.3 ± 7.2 |
| Female | 1,549 (72.3%) | Drinking (n, %) | No | 1,898 (88.6%) | |
| Education level (n, %) | Junior college | 1,272 (59.4%) | Yes | 244 (11.4%) | |
| College | 748 (34.9%) | If drinking, frequency of drinking (n, %) | Once a month | 171 (70.1%) | |
| Postgraduate | 122 (5.7%) | 2∼4 times per month | 68 (27.9%) | ||
| Marital status (n, %) | Single | 2,121 (99.0%) | 2∼3 times per week | 5 (2.0%) | |
| Married | 21 (1.0%) | If drinking, the amount of drinking in a day (n, %) | 1 or 2 cups | 170 (69.7%) | |
| Nationality (n, %) | Han | 2,048 (95.6%) | 3 or 4 cups | 40 (16.4%) | |
| Hui | 35 (1.6%) | 5 or 6 cups | 15 (6.1%) | ||
| Manchu | 8 (0.4%) | 7∼9 cups | 7 (2.9%) | ||
| Yi ethnic group | 8 (0.4%) | ⩾10 cups | 12 (4.9%) | ||
| Mongolian | 7 (0.3%) | ||||
| Tujia | 7 (0.3%) | ||||
| Others | 29 (1.3%) | ||||
| Grade (n, %) | Freshman year | 915 (42.7%) | Sleep duration (Median ± SD) | 6.4 ± 1.0 | |
| Sophomore year | 702 (32.8%) | <5 h | 116 (5.4%) | ||
| Junior year | 285 (13.3%) | 5∼6 h | 449 (21.0%) | ||
| Senior year | 80 (3.7%) | 6∼7 h | 1,055 (49.3%) | ||
| University grade five | 38 (1.8%) | 7∼8 h | 460 (21.5%) | ||
| Postgraduate grade | 122 (5.7%) | 8∼9 h | 46 (2.1%) | ||
| ≥9 h | 16 (0.7%) | ||||
| Nap duration (n, %) | 0∼15 min | 580 (27.1%) | |||
| 16∼30 min | 953 (44.5%) | ||||
| 31∼60 min | 514 (24.0%) | ||||
| >60 min | 95 (4.4%) |