Table 2.

Trends in the least square mean (± standard error) values for body mass index and waist circumference according to household income and urbanity

	1998–2001	2010–2012	P for trends*	P for interaction**
Body mass index
Boys	20.42 (0.09)	20.76 (0.11)	0.0195
Household income
Low	20.09 (0.15)	20.38 (0.20)	0.2431	0.3864
Middle	20.46 (0.15)	20.73 (0.19)	0.2676
High	20.67 (0.16)	21.28 (0.20)	0.0175
P-value for trend***	0.0101	0.0017
Urbanity
Rural	19.96 (0.18)	20.31 (0.27)	0.291	0.9616
Urban	20.52 (0.10)	20.86 (0.13)	0.0379
P-value****	0.0087	0.083
Girls	20.01 (0.08)	20.14 (0.11)	0.3435
Household income
Low	20.34 (0.16)	20.26 (0.19)	0.7782	0.7072
Middle	19.86 (0.13)	20.17 (0.18)	0.1607
High	19.87 (0.14)	19.94 (0.18)	0.7738
P-value for trend***	0.0215	0.188
Urbanity
Rural	20.03 (0.17)	20.47 (0.32)	0.2438	0.3532
Urban	20.00 (0.10)	20.07 (0.11)	0.6463
P-value****	0.5636	0.1752
Waist circumference (cm)
Boys	71.59 (0.25)	70.75 (0.30)	0.0308
Household income
Low	70.93 (0.43)	69.98 (0.51)	0.1527	0.3942
Middle	71.57 (0.41)	70.37 (0.49)	0.0592
High	72.20 (0.45)	72.13 (0.56)	0.9133
P-value for trend***	0.039	0.0053
Urbanity
Rural	70.32 (0.48)	69.69 (0.73)	0.4722	0.7682
Urban	71.87 (0.28)	70.97 (0.33)	0.0385
P-value****	0.0071	0.1363
Girls	67.41 (0.22)	66.85 (0.26)	0.0952
Household income
Low	68.46 (0.39)	67.09 (0.46)	0.0244	0.1762
Middle	67.18 (0.36)	66.94 (0.41)	0.6587
High	66.69 (0.36)	66.41 (0.42)	0.62
P-value for trend***	0.0007	0.2872
Urbanity
Rural	67.25 (0.42)	67.83 (0.71)	0.4802	0.122
Urban	67.44 (0.25)	66.63 (0.27)	0.0272
P-value****	0.8649	0.0869

*P-values for time trends between 1998–2001 and 2010–2012

**P-values for the interactions between time period and household income and between time period and urbanity

***P-values for linear trends among household income groups

****P-values for between-group (urban-rural areas) differences