Table 1. General characteristics of study participants.
| Variables | Boys (n = 28,501) | Girls (n = 27,230) | Total (n = 55,731 ) | P-value |
| Age (years) | n (%) | n (%) | n (%) | <0.0001 |
| 12 | 1,402 (4.9) | 1,460 (5.4) | 2,862 (5.1) | |
| 13 | 4,494 (15.8) | 4,155 (15.3) | 8,649 (15.5) | |
| 14 | 4,714 (16.5) | 4,418 (16.2) | 9,132 (16.4) | |
| 15 | 4,954 (17.4) | 4,658 (17.1) | 9,612 (17.3) | |
| 16 | 5,070 (17.8) | 4,878 (17.9) | 9,948 (17.9) | |
| 17 | 5,020 (17.6) | 4,967 (18.2) | 9,987 (17.9) | |
| 18 | 2,847 (10.0) | 2,694 (9.9) | 5,541 (9.9) | |
| Current smoking | <0.0001 | |||
| Nonsmoking | 2,3807 (83.5) | 25,514 (93.7) | 49,321 (88.5) | |
| Smoking | 4,694 (16.5) | 1,716 (6.3) | 6,410 (11.5) | |
| Current alcohol consumption | <0.0001 | |||
| Nondrinking | 21,633 (75.9) | 22,176 (81.4) | 43,809 (78.6) | |
| Drinking | 6,868 (24.1) | 5,054 (18.6) | 11,922 (21.4) | |
| Educational level of mother | <0.0001 | |||
| Middle school or lower | 1,927 (6.8) | 1,859 (6.8) | 3,786 (6.8) | |
| High school | 15,699 (55.1) | 15,765 (57.9) | 31,464 (56.5) | |
| College or higher | 10,875 (38.2) | 9,606 (35.3) | 20,481 (36.8) | |
| Educational level of father | <0.0001 | |||
| Middle school or lower | 1,988 (7.0) | 1,796 (6.6) | 3,784 (6.8) | |
| High school | 12,028 (42.2) | 11,930 (43.8) | 23,958 (43.0) | |
| College or higher | 14,485 (50.8) | 13,504 (49.6) | 27,989 (50.2) | |
| Economic status | <0.0001 | |||
| Very wealthy | 2,529 (8.9) | 1,309 (4.8) | 3,838 (6.9) | |
| Wealthy | 7,447 (26.1) | 6,301 (23.1) | 13,748 (24.7) | |
| Average | 12,709 (44.6) | 13,517 (49.6) | 26,226 (47.1) | |
| Poor | 4,477 (15.7) | 4,921 (18.1) | 9,398 (16.9) | |
| Very poor | 1,339 (4.7) | 1,182 (4.3) | 2,521 (4.5) | |
| Living situation | <0.0001 | |||
| Living with family | 27,133 (95.2) | 26,070 (95.7) | 53,203 (95.5) | |
| Living with relatives | 319 (1.1) | 283 (1.0) | 602 (1.1) | |
| Boarding house, living alone, dormitory | 963 (3.4) | 841 (3.1) | 1,804 (3.2) | |
| Facilities* | 86 (0.3) | 36 (0.1) | 122 (0.2) | |
| City type | <0.0001 | |||
| Large city | 13,958 (49.0) | 12,776 (46.9) | 26,734 (48.0) | |
| Mid-sized city | 10,750 (37.7) | 10,953 (40.2) | 21,703 (38.9) | |
| Small city | 3,793 (13.3) | 3,501 (12.9) | 7,294 (13.1) | |
| Stress | <0.0001 | |||
| Very high | 2,872 (10.1) | 4,101 (15.1) | 6,973 (12.5) | |
| High | 7,708 (27.0) | 9,550 (35.1) | 17,258 (31.0) | |
| Moderate | 12,409 (43.5) | 10,407 (38.2) | 22,816 (40.9) | |
| Low | 4,613 (16.2) | 2,860 (10.5) | 7,473 (13.4) | |
| None | 899 (3.2) | 312 (1.15) | 1,211 (2.2) | |
| Atopic dermatitis with severity † | <0.0001 | |||
| 0 | 22,951 (80.5) | 20,266 (74.4) | 43,217 (77.6) | |
| 1 | 5,317 (18.7) | 6,798 (25.0) | 12,115 (21.7) | |
| 2 | 151 (0.5) | 110 (0.4) | 261 (0.5) | |
| 3 | 36 (0.1) | 27 (0.1) | 63 (0.1) | |
| 4 | 46 (0.2) | 29 (0.1) | 75 (0.1) |
*
Facilities: an organization for social welfare and an orphanage.
†
Atopic dermatitis with severity: (0) no atopic dermatitis, (1) having atopic dermatitis but no school absence, (2) 1–3 days of school absence with atopic dermatitis, (3) 4–6 days of school absence with atopic dermatitis, and (4) more than 7 days of school absence with atopic dermatitis.