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Table 2 Descriptive statistics of children and their households participating in the current study

From: Socio-demographic and lifestyle factors for child’s physical growth and adiposity rebound of Japanese children: a longitudinal study of the 21st century longitudinal survey in newborns

  All Boys Girls
Variable Age at survey† N Mean SD N Mean SD N Mean SD
Body mass index (kg/m2) At birth 45284 12.62 1.23 23542 12.65* 1.23 21742 12.58* 1.24
  1 ½ years 38422 16.33 1.45 19939 16.52* 1.43 18483 16.13* 1.44
  2 ½ years 33672 16.09 1.45 17523 16.21* 1.43 16149 15.96* 1.45
  3 ½ years 36146 15.75 1.33 18797 15.82* 1.32 17349 15.66* 1.33
  4 ½ years 35097 15.48 1.36 18265 15.52* 1.34 16832 15.44* 1.37
  5 ½ years 33057 15.38 1.50 17212 15.43* 1.50 15845 15.34* 1.50
Variable Age at survey † Unit/category N Mean (SD) or %       
Parents’ annual income ½ year (million yen) 45383 5.30 (3.28)       
  4 ½ years   36922 5.77 (3.47)       
Sleep hour           
  4 ½ years (hours) 36026 9.9 (0.8)       
Expense for child           
  ½ year (10,000 yen/month) 44093 2‡ (0, 400)‡       
  4 ½ years   37347 4‡ (0, 447)‡       
Gestational period -- 22-36 weeks 45392 5.1       
   37-41 weeks   94.1       
   ≥ 42 weeks   0.9       
Birth weight -- < 1000 g 45392 0.2       
   1001-1500 g   0.4       
   1501-2500 g   7.9       
   ≥ 2501 g   91.5       
Main parental care provider ½ year Mother 45316 92.2       
   Father   0.1       
   Grandmother   3.7       
   Grandfather   0.1       
   Others   3.9       
  4 ½ years Mother 38296 40.9       
   Father   0.3       
   Grandmother   2.4       
   Grandfather   0.2       
   Others   56.3       
Sibling ½ year No sibling 45392 49.6       
   With sibling   50.4       
  4 ½ years No sibling 38715 18.7       
   With sibling   81.3       
Household member ½ year With grandparent (s) and parent(s) 45392 21.6       
   With both parents   77.9       
   With a parent   0.4       
   Other   0.1       
  4 ½ years With grandparent(s) and parent(s) 38715 23.0       
   With both parents   73.9       
   With a parent   3.0       
   Other   0.2       
Wake-up time 4 ½ years Before 7 am 38634 25.1       
   7 am-   60.7       
   8 am-   11.0       
   9 am-   1.0       
   Irregular   2.2       
Television watching§ 4 ½ years None 37377 1.1       
   < 1 hour   15.9       
   1 hour   40.2       
   2 hours   28.1       
   3 hours   10.5       
   4 hours   3.2       
   ≥ 5 hours   1.0       
Video game playing 4 ½ years None 37240 60.5       
   < 1 hour   29.7       
   1 hour   8.5       
   2 hours   1.1       
   3 hours   0.3       
Breakfast 4 ½ years Eating regularly 45392 97.7       
   Eating irregularly   1.6       
   Don’t eat   0.7       
Lunch 4 ½ years Eating regularly 45392 99.4       
   Eating irregularly   0.6       
   Don’t eat   0.0       
Dinner 4 ½ years Eating regularly 45392 97.4       
   Eating irregularly   2.6       
   Don’t eat   0.1       
Snack 4 ½ years Eating regularly 45392 90.8       
   Eating irregularly   7.9       
   Don’t eat   1.3       
  1. *Statistically significant at the level of P < .05 in a two-sided t-test between genders.
  2. †Survey time points were at approximate mean ages.
  3. ‡We described the median, the maximum, and the minimum values because the data did not follow a normal distribution.
  4. §Spearman’s correlation with time spent playing video games was 0.124 (P < .01).
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