Table. Characteristics of study subjects by grade and sex.
| Fourth graders | Seventh graders | ||||||
| Boys (n = 2269) | Girls (n = 2098) | P-value | Boys (n = 1910) | Girls (n = 1814) | P-value | ||
| Age (years) | Mean (SD) | 9.3 (0.4) | 9.3 (0.4) | 0.560 | 12.2 (0.4) | 12.2 (0.4) | 0.697 |
| Height (cm) | Mean (SD) | 134.4 (5.7) | 134.4 (6.3) | 0.813 | 154.0 (8.2) | 152.5 (6.0) | <0.001 |
| Weight (kg) | Mean (SD) | 31.0 (6.3) | 30.2 (6.0) | <0.001 | 44.5 (9.9) | 43.7 (8.0) | 0.010 |
| BMI (kg/m2) | Mean (SD) | 17.1 (2.6) | 16.6 (2.3) | <0.001 | 18.6 (3.0) | 18.7 (2.8) | 0.290 |
| Median (IQR: Q3 to Q1) | 16.5 (18.1 to 15.3) | 16.2 (17.7 to 15.1) | 17.9 (19.7 to 16.6) | 18.3 (20.0 to 16.8) | |||
| Range (Max to Min) | 23.6 (35.5 to 11.9) | 18.9 (30.9 to 12.0) | 25.5 (38.3 to 12.9) | 24.0 (36.6 to 12.6) | |||
| POW (%) | Mean (SD) | 0.2 (14.1) | −1.0 (13.0) | 0.003 | −0.8 (15.4) | −2.3 (14.1) | 0.001 |
| Median (IQR: Q3 to Q1) | −2.5 (6.3 to −9.2) | −3.5 (5.3 to −9.8) | −4.1 (4.5 to −10.6) | −4.6 (4.4 to −11.4) | |||
| Range (Max to Min) | 119.1 (91.2 to −27.9) | 100.4 (73.0 to −27.5) | 132.9 (100.6 to −32.3) | 116.0 (85.6 to −30.4) | |||
| Criteria | |||||||
| BMIa | Underweight (%) | 8.9 | 12.0 | <0.001 | 8.3 | 10.7 | 0.002 |
| Normal weight (%) | 76.0 | 76.4 | 77.4 | 78.1 | |||
| Overweight (%) | 15.1 | 11.6 | 14.3 | 11.2 | |||
| POWb | Underweight (%) | 2.0 | 2.1 | 0.152 | 3.3 | 6.2 | <0.001 |
| Normal weight (%) | 89.6 | 90.9 | 87.0 | 86.8 | |||
| Overweight (%) | 8.5 | 6.9 | 9.7 | 7.0 | |||
BMI, body mass index; IQR, interquartile range; Max to Min, maximum to minimum; Q3 to Q1, 75th percentile to 25th percentile; SD, standard deviation.
aBMI cutoff points as defined by the International Obesity Task Force.
bPOW (percentage of overweight) as defined by the Japanese Ministry of Education, Culture, Sports, Science and Technology.
The unpaired t test and chi-square test were used to compare characteristics between boys and girls.