Table 2 Demographic characteristics of the sample (%)

Age (M [SD])Grade

12.46[0.96]

12.51[0.98]

12.40[0.93]

0.013

  6

34.06

33.41

34.73

  7

37.24

36.42

38.08

0.395

  8

28.71

30.17

27.19

Has siblings

  Yes

35.41

36.98

33.89

0.198

  No

64.59

63.12

64.59

Locally registered resident

  Yes

79.29

77.80

80.84

0.298

  No

20.71

22.20

19.16

Rents a house

  Yes

18.35

20.12

16.53

0.056

  No

81.65

79.88

83.47

Highest parental education

  Junior high school and below

10.76

12.49

8.98

  High/technical school

26.53

25.78

27.31

  College/university

50.41

49.13

51.74

0.115

  Unknown

12.29

12.60

11.98

Parental divorce

  Yes

11.47

10.06

12.93

0.063

  No

88.53

89.94

88.53