# Table 2 Comparisons of characteristics between the normal weight and underweight groups in boys (Japan, 2001–2008)

Normal weight (n = 933) Underweight (n = 99) P valuea
Age (years) 12.0 (12.0, 13.0) 12.0 (12.0, 13.0) 0.186
Birthweight (g), n (%)
< 2500 50 (5.4) 10 (10.1) 0.055
≥ 2500 883 (94.6) 89 (89.9)
Height (cm) 155.5 (149.2, 160.8) 149.9 (144.6, 154.7) <0.001
Weight (kg) 43.7 (39.1, 48.3) 33.0 (30.8, 36.2) <0.001
Body mass index (kg/m2) 18.0 (16.9, 19.2) 15.0 (14.6, 15.3) <0.001
Exercise, n (%)
Daily 788 (84.5) 81 (81.8) 0.325
Sometimes 71 (7.6) 6 (6.1)
None 74 (7.9) 12 (12.1)
Skipping breakfast, n (%)
Yes 45 (4.8) 3 (3.0) 0.421
No 888 (95.2) 96 (97.0)
Snacking after dinner, n (%)
Always or often 580 (62.2) 57 (57.6) 0.372
Seldom or none 353 (37.8) 42 (42.4)
Snacking while watching television or reading books, n (%)
Yes 383 (41.1) 34 (34.3) 0.196
No 550 (59.0) 65 (65.7)
Eating slowly, n (%)
Yes 161 (17.3) 35 (35.4) <0.001
No 772 (82.7) 64 (64.7)
1. Except where indicated n (%), values are expressed as median (25, 75th percentile)
2. aWilcoxon rank-sum test or chi-square test