Table 1 Descriptive characteristics of the study population
|  | Whole sample (n = 825) | Boys (n = 359) | Girls (n = 466) | p-gender difference |
|---|---|---|---|---|
Age (y) | 15.0 ± 0.301 | 15.0 ± 0.31 | 15.0 ± 0.29 | 0.87 |
Pubertal status (n (%))2,3 | Â | Â | Â | Â |
   Pre-pubertal | 79 (9.8) | 71 (20.7) | 8 (1.7) |  |
   Pubertal | 730 (90.2) | 272 (79.3) | 458 (98.3) | <0.001 |
Ethnicity (n (%))4 | Â | Â | Â | Â |
   White | 767 (94.6) | 341 (95.8) | 426 (93.6) |  |
   Other | 44 (5.4) | 15 (4.2) | 29 (6.4) | 0.18 |
Area-level SES (n (%)) | Â | Â | Â | Â |
   Low | 124 (15.0) | 62 (17.3) | 62 (13.3) |  |
   Middle | 193 (23.4) | 80 (22.3) | 113 (24.3) |  |
   High | 508 (61.6) | 217 (60.5) | 291 (62.5) | 0.27 |
Height (cm) | 166.5 ± 7.9 | 171.4 ± 7.7 | 162.8 ± 5.8 | <0.001 |
Weight (kg) | 55.7 (13.3)5 | 57.8 (13.6) | 53.9 (12.3) | <0.001 |
BMI (kg/m2) | 20.1 (3.9) | 19.7 (3.5) | 20.3 (4.1) | 0.0011 |
Fat mass (kg) | 11.5 (7.8) | 8.2 (5.3) | 13.7 (6.9) | <0.001 |
Fat mass index (kg/m2) | 4.2 (3.0) | 2.8 (1.8) | 5.2 (2.5) | <0.001 |
Overfat (%)6 | 123 (14.9) | 53 (14.8) | 70 (15.0) | 0.92 |
Sleep duration (min/d) | 493.7 ± 52.8 | 487.9 ± 48.8 | 498.2 ± 55.4 | <0.01 |