Table 2 Associations between socio-demographic factors and IA^a,b

School grade

 Secondary 1

12.23

1.00

9.30

1.00

 Secondary 2

17.83

1.56 (1.25 ~ 1.95)

13.88

1.57 (1.20 ~ 2.07)

 Secondary 3

19.69

1.76 (1.42 ~ 2.18)*

14.61

1.67 (1.28 ~ 2.18)

 Secondary 4

20.75

1.88 (1.51 ~ 2.34)**

17.67

2.09 (1.61 ~ 2.71)**

Father’s education level

 Junior secondary school or below

21.76

1.00

15.34

1.00

 Senior secondary school or matriculation

17.14

0.74 (0.62 ~ 0.89)**

13.81

0.88 (0.72 ~ 1.08)

 University or college or above

12.34

0.51 (0.40 ~ 0.64)**

12.69

0.80 (0.61 ~ 1.06)

 Missing

17.99

0.79 (0.64 ~ 0.98)*

13.30

0.85 (0.65 ~ 1.10)

Mother’s education level

 Junior secondary school or below

23.09

1.00

15.52

1.00

 Senior secondary school or matriculation

16.01

0.64 (0.54 ~ 0.76)**

13.63

0.86 (0.71 ~ 1.05)

 University or college or above

12.68

0.48 (0.38 ~ 0.62)**

10.72

0.65 (0.47 ~ 0.90)*

 Missing

17.28

0.70 (0.56 ~ 0.86)**

14.45

0.92 (0.71 ~ 1.19)

Living arrangement with parents

 Living with both parents

16.46

1.00

13.09

1.00

 Living with the mother only

22.44

1.47 (1.16 ~ 1.85)**

18.58

1.52 (1.17 ~ 1.96)**

 Living with the father only

30.82

2.26 (1.60 ~ 3.20)**

20.97

1.76 (1.13 ~ 2.74)*

 Living with none of the parents

20.00

1.27 (0.83 ~ 1.95)

17.01

1.36 (0.88 ~ 2.11)

 Missing

20.56

1.31 (0.82 ~ 2.12)

14.75

1.15 (0.56 ~ 2.35)

Father’s age

Not applicable

1.01 (0.99 ~ 1.02)

Not applicable

1.01 (0.99 ~ 1.02)

Whether born in HK/length of stay

 Yes, born in HK

17.01

1.00

13.88

1.00

 No, stayed in HK ≥7 years

20.74

1.28 (1.03 ~ 1.58)*

15.02

1.10 (0.86 ~ 1.40)

 No, stayed in HK <7 years

19.93

1.21 (0.90 ~ 1.65)

13.37

0.96 (0.69 ~ 1.34)

 No, don’t remember when came to HK

16.83

0.99 (0.58 ~ 1.67)

12.33

0.87 (0.43 ~ 1.77)

 Missing

21.05

1.30 (0.59 ~ 2.85)

23.81

1.94 (0.71 ~ 5.32)