Table 1. Descriptive statistics of the panel dataa .
| Waves | P valueb | ||||
| 2007 | 2008 | 2009 | 2010 | ||
| Number of subjects | 1687 | 1687 | 1687 | 1687 | |
| Age (years) | 33.4 (5.0) | 34.4 (5.0) | 35.4 (5.0) | 36.5 (5.0) | 0.000 |
| BMI (kg/m2) | 23.5 (3.3) | 23.5 (3.2) | 23.6 (3.3) | 23.7 (3.4) | 0.000 |
| Obesity (BMI of ≥25.0 kg/m2) (%) | 26.6 | 26.2 | 28.2 | 29.4 | 0.000 |
| Sleep duration (hours) | 5.93 (0.82) | 5.92 (0.82) | 5.88 (0.85) | 5.89 (0.83) | 0.002 |
| Drinking habit (%) | 84.4 | 85.5 | 86.4 | 86.1 | 0.001 |
| Alcohol (g/week) | 114.6 (116.9) | 125.7 (127.3) | 128.2 (130.9) | 130.6 (125.6) | 0.000 |
| Exercise habit (%) | 48.1 | 47.3 | 47.1 | 46.9 | 0.288 |
| Smoking habit (%) | 40.8 | 39.9 | 39.7 | 37.8 | 0.000 |
| Psychiatric medication (%) | 0.2 | 0.3 | 0.2 | 0.2 | 0.896 |
| Depressive symptoms (%) | 5.3 | 5.0 | 5.1 | 4.9 | 0.579 |
| Ill health (%) | 2.5 | 2.3 | 2.0 | 2.4 | 0.731 |
| Sleep disturbance (%) | 3.2 | 2.9 | 2.7 | 2.5 | 0.159 |
| Midmorning sleepiness (%) | 3.6 | 3.8 | 3.6 | 3.0 | 0.285 |
| Midmorning fatigue (%) | 4.5 | 5.0 | 4.9 | 4.2 | 0.511 |
BMI, body mass index.
aData are expressed as means (standard deviation) or percentages. Each percentage was calculated without missing data.
bChange trends in the characteristics of the subjects among the different waves were examined using generalized estimating equations with each variable as a dependent variable and waves as a continuous independent variable to take into account the repeated measurements.