Table 1. Characteristics of 249 Korean male high school students.
| Characteristics | No. of students (%) or mean ± SD | |
|---|---|---|
| Age, yr | 17 | 133 (53.4) |
| 18 | 60 (24.1) | |
| 19 | 56 (22.5) | |
| Experience of smoking | No | 232 (93.2) |
| Yes | 17 (6.8) | |
| Experience of alcohol drinking | No | 214 (85.9) |
| Yes | 35 (14.1) | |
| Regular physical activity | No | 77 (30.9) |
| Yes | 172 (69.1) | |
| Weight loss attempts | No | 202 (81.1) |
| Yes | 47 (18.9) | |
| Experience of working for making money | No | 193 (77.5) |
| Yes | 56 (22.5) | |
| Caffeinated beverage consumption | No | 18 (7.2) |
| Yes | 231 (92.8) | |
| Consumption of specific caffeinated beverages, cup/day | Coffee | 0.4 ± 0.4 |
| Tea | 0.3 ± 0.6 | |
| Soft drink | 0.4 ± 0.3 | |
| Energy drink | 0.2 ± 0.3 | |
| Chocolate/cocoa drink | 0.2 ± 0.6 | |
| Having screen time | No | 7 (2.8) |
| Yes | 242 (97.2) | |
| Time spent for specific screen media, hr/day | TV | 0.7 ± 0.7 |
| DVD movies | 0.3 ± 0.6 | |
| Computer | 1.3 ± 0.7 | |
| Mobile phone | 1.5 ± 0.7 | |
| Screen games | 0.5 ± 0.7 | |
| Average screen time, hr/day | 4.4 ± 1.9 | |
| Average sleep duration, hr/day | 6.9 ± 1.1 | |
| ESS scores | ≤ 6 | 157 (63.0) |
| 7–8 | 44 (17.7) | |
| ≥ 9 | 48 (19.3) |
SD, standard deviation; ESS, Epworth Sleepiness Scale.