Table 1a.
Characteristics of the study sample
| Individual level | Boys | Girls | Total | P value |
| Mean±SD or n (%) | ||||
| No of students, n (%) | 1279 (49.5) | 1307 (50.5) | 2586 | |
| Age (years, mean±SD) (n=2586) | 12.5±0.5 | 12.4±0.5 | 12.4±0.5 | <0.001 |
| 12 years, n (%) | 651 (50.9) | 775 (59.3) | 1426 (55.1) | <0.001 |
| 13 years, n (%) | 628 (49.1) | 532 (40.7) | 1160 (44.9) | |
| Height (cm, mean±SD) (n=2440) | 161.1±9.5 | 160.1±7.3 | 160.6±8.4 | 0.003 |
| Weight (kg, mean±SD) (n=2360) | 49.5±10.9 | 47.0±8.9 | 48.3±10.0 | <0.001 |
| BMI* (kg/m2, mean±SD) (n=2296) | 18.9±3.1 | 18.3±2.7 | 18.6±2.9 | <0.001 |
| BMI range | 11.8–30.9 | 11.7–33.8 | 11.7–33.8 | |
| Underweight (BMI <10th percentile)† | 126 (11.1) | 218 (18.8) | 344 (15.0) | <0.001 |
| Normal weight (BMI 10th to <90th percentile)† | 822 (72.2) | 843 (72.6) | 1665 (72.4) | |
| Overweight (BMI 90th to <97th percentile)† | 166 (14.6) | 90 (7.8) | 256 (11.1) | |
| Obesity (BMI ≥97th percentile)† | 24 (2.1) | 10 (0.9) | 34 (1.5) | |
| Migrant background (n=2423) | 396 (33.1) | 429 (35.0) | 825 (34.0) | 0.307 |
| Individual SES (Family Affluence Scale; FAS) (n=2139) | ||||
| High (FAS 6–7) | 569 (53.7) | 500 (46.3) | 1069 (50.0) | 0.003 |
| Moderate (FAS 4–5) | 371 (35.0) | 441 (40.9) | 812 (38.0) | |
| Low (FAS 0–3) | 120 (11.3) | 138 (12.8) | 258 (12.1) | |
| Students’ neighbourhood SES (n=2240) | 1114 | 1126 | 2240 | |
| Mean±SD | 4.0±1.9 | 4.1±1.9 | 4.0±1.9 | 0.526 |
| 1 (best) | 127 (11.4) | 123 (10.9) | 250 (11.2) | |
| 2 | 182 (16.3) | 194 (17.2) | 376 (16.8) | |
| 3 | 143 (12.8) | 119 (10.6) | 262 (11.7) | |
| 4 | 215 (19.3) | 229 (20.3) | 444 (19.8) | |
| 5 | 162 (14.5) | 160 (14.2) | 322 (14.4) | |
| 6 | 134 (12.0) | 134 (11.9) | 268 (12.0) | |
| 7 (worst) | 151 (13.6) | 167 (14.8) | 318 (14.2) | |
| School type (n=2586) | ||||
| High school‡ students (15 schools) | 507 (39.6) | 624 (47.7) | 1131 (43.7) | <0.001 |
| Integrated secondary school§ students (32 schools) | 772 (60.4) | 683 (52.3) | 1455 (56.3) | |
Descriptive statistical methods.
*Body mass index (kg/m2).
†BMI percentiles according to Cole et al.39 40
‡High schools (5th or 7th grade to 12th grade, graduation with high school diploma after 12th grade).
§Integrated secondary schools (integration of different school types, 7th grade to 13th grade, graduation with secondary school leaving certificate after 10th grade or high school diploma after 13th grade).
SES, socioeconomic status.