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Table 6 The generalized estimating equation (GEE) of BMI for six-year surveys including all candidate exploratory factors

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

Variable Category Estimate 95% confidence interval P value P value in type 3 effect analysis§
BMI at baseline survey   0.150 0.139 0.161 <.01* <.01*
Age   -0.263 -0.269 -0.258 <.01* <.01*
Overweight at age 5 ½ years (base category; < 85th percentile)   1.736 1.703 1.770 <.01* <.01*
Gender (base category; boy) Girl -0.167 -0.189 -0.145 <.01* <.01*
Gestational period < 22–36 weeks 0.170 0.115 0.225 <.01* <.01*
(Base category; 37–41 weeks) ≥ 42 weeks -0.159 -0.278 -0.039 <.01* <.01*
Main parental care provider at age 6 months Father -0.088 -0.383 0.208 .56  
(Base category; mother) Grandmother 0.004 -0.061 0.069 .91  
  Grandfather -0.012 -0.349 0.326 .95  
  Others 0.123 0.061 0.184 <.01*  
Main parental care provider across the surveys Father -0.094 -0.249 0.061 .24 <.01*
(Base category; mother) Grandmother -0.065 -0.112 -0.017 .01*  
  Grandfather 0.115 -0.052 0.283 .18  
  Others 0.084 0.067 0.100 <.01*  
Sibling at age 6 months (base category; no sibling) With sibling 0.018 -0.008 0.043 .17 .17
Sibling across the surveys (base category; no sibling) With sibling -0.011 -0.032 0.011 .34 .34
Household member at age 6 months With both parents -0.026 -0.061 0.009 .15 .21
(base category; with grandparent(s) and parent(s)) With a parent 0.069 -0.107 0.244 .45  
  Other -0.673 -1.285 -0.061 .03*  
Household member across the surveys With both parents -0.027 -0.058 0.004 .09 .33
(Base category; with grandparent(s) and parent(s)) With a parent -0.040 -0.103 0.024 .22  
  Other -0.079 -0.334 0.175 .54  
Parents’ income at age 6 months 4,610,000 yen-(42,000 dollars-) -0.001 -0.033 0.030 .94 .79
(Base category; < 4,610,000 yen (about 42,000 dollars)) 5,870,000 yen-(53,000 dollars -) 0.009 -0.027 0.046 .61  
  6,970,000 yen-(63,000 dollars -) 0.020 -0.019 0.058 .31  
  8,650,000 yen-(79,000 dollars -) 0.000 -0.047 0.046 .99  
Parents’ income at age 4 ½ years 4,660,000 yen-(42,000 dollars -) 0.022 -0.009 0.054 .16 .16
(Base category; < 4,660,000 yen (about 42,000 dollars)) 5,770,000 yen-(52,000 dollars -) 0.033 -0.003 0.069 .07  
  6,810,000 yen-(62,000 dollars -) 0.007 -0.031 0.046 .71  
  8,380,000 yen-(76,000 dollars -) 0.045 0.000 0.090 .05  
Expense for kid at age 6 months   0.000 -0.001 0.002 .61 .61
Expense for kid across the surveys   0.000 -0.001 0.001 .56 .56
Wake-up time (base time; 0 am)   -0.040 -0.061 -0.019 <.01* <.01*
Sleeping hours   0.004 -0.013 0.020 .66 .66
Television watching < 1 hour -0.040 -0.142 0.061 .44 .13
  1 hour - -0.045 -0.145 0.056 .38  
  2 hour - -0.050 -0.151 0.051 .34  
  3 hour - 0.004 -0.101 0.110 .94  
  4 hour - 0.000 -0.118 0.119 1.00  
  5 hour - 0.033 -0.136 0.202 .70  
Video game playing < 1 hour 0.013 -0.012 0.038 .31 .04*
  1 hour - 0.067 0.025 0.109 <.01*  
  2 hour - 0.024 -0.098 0.145 .70  
  3 hour - -0.062 -0.328 0.205 .65  
Breakfast at age 4 ½ years Eating irregularly -0.115 -0.246 0.015 .08 .22
(Base category; eating regularly) Don’t eat 0.013 -0.143 0.169 .87  
Lunch at age 4 ½ years Eating irregularly 0.094 -0.115 0.303 .38 .63
(Base category; eating regularly) Don’t eat -0.177 -1.077 0.723 .70  
Dinner at age 4 ½ years Eating irregularly 0.008 -0.081 0.097 .86 .96
(Base category; eating regularly) Don’t eat -0.046 -0.462 0.369 .83  
Snack at age 4 ½ years Eating irregularly -0.053 -0.092 -0.013 <.01* .03*
(Base category; eating regularly) Don’t eat -0.026 -0.138 0.086 .65  
  1. *Statistically significant at the level of P < .05.
  2. BMI: body mass index.
  3. The threshold parents’ incomes shown in Japanese yen were converted to the US dollar by purchasing power parity rate (1 dollar = 110 yen).
  4. §Type 3 effect test is based on an asymptotic chi-square distribution of the likelihood ratio statistic computed from GEE models and it allows one to test for an effect of interest provided all the other variables are included in the GEE model.
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