Table 1. Demographic characteristics of participants (n = 886).
| Mean (SD) or n (%) | ||
| Sex, boy | 473 (53.4) | |
| Age, mean (SD) | 11.9 (3.3) | |
| 7–12 | 510 (57.6) | |
| 13–18 | 376 (42.4) | |
| Number of siblings | ||
| 0 | 121 (13.7) | |
| 1 | 501 (56.5) | |
| ≥2 | 264 (29.8) | |
| BMI, kg/m2, mean (SD) | 17.6 (2.8) | |
| Exercise time, min/week | 314 (430) | |
| Parents’ educational attainment,a year | ||
| Father, | ≤12 | 233 (26.3) |
| 13–15 | 73 (8.2) | |
| ≥16 | 580 (65.5) | |
| Mother, | ≤12 | 247 (27.9) |
| 13–15 | 412 (46.5) | |
| ≥16 | 227 (25.6) | |
| Equivalent household income,b JPY/year | ||
| Low (<2,795,085) | 222 (25.1) | |
| Middle (2,795,085–3,913,119) | 276 (31.1) | |
| High (>3,913,119) | 388 (43.8) | |
| Parental working hours,a hours/week | ||
| Father, mean (SD) | 41.3 (23.2) | |
| 0 | 15 (1.7) | |
| 1–47 | 435 (49.1) | |
| ≥48 | 436 (49.2) | |
| Mother, mean (SD) | 12.6 (15.6) | |
| 0 | 394 (44.5) | |
| 1–19 | 215 (24.2) | |
| ≥20 | 277 (31.3) | |
| Sedentary behavior on weekdays, min/day | ||
| Total sedentary time | 222 (123) | |
| Screen time | 144 (108) | |
| TV/Video/DVD | 89 (72) | |
| Game | 33 (46) | |
| Internet | 23 (41) | |
| Non-Screen time | 78 (65) | |
| Reading/Music | 27 (36) | |
| Study | 51 (51) | |
BMI, body mass index; SD, standard deviation.
aParents were counted several times if they have multiple children.
bCalculated by dividing household annual income by the square root of the number of household members.