Table 3 Multilevel zero-inflated negative binomial regression models for DMFT score in children aged 12 years in China in 2005 and 2015 surveys

Level-1 indicators

Sex

Female (vs. Male)

1.19(1.09-1.30)

0.0001

1.23(1.17-1.29)

<0.0001

1.22(1.17-1.27)

<0.0001

Ethnicity

Other (vs. Han)

1.11(0.96-1.28)

0.15

0.96(0.88-1.04)

0.30

0.99(0.92-1.07)

0.78

Location of residence

Rural (vs. Urban)

1.06(0.96-1.16)

0.24

1.01(0.96-1.07)

0.59

1.03(0.99-1.08)

0.14

Only child

Yes (vs. No)

0.95(0.86-1.05)

0.29

0.96(0.92-1.01)

0.11

0.98(0.93-1.02)

0.33

Parental highest education attainment (vs. Junior high school or below)

High school

1.05(0.92-1.19)

0.47

1.02(0.95-1.11)

0.54

1.04(0.97-1.11)

0.29

Tertiary or bachelor degree or above

1.11(0.94-1.30)

0.22

1.02(0.93-1.12)

0.63

1.04(0.96-1.13)

0.30

Unknown or orphan

1.06(0.85-1.31)

0.62

1.04(0.95-1.15)

0.39

1.05(0.96-1.15)

0.27

Toothbrushing frequency

Twice or more per day (vs. Once a day or less)

0.92(0.83-1.01)

0.087

1.02(0.98-1.06)

0.40

1.01(0.97-1.06)

0.60

Use of dental floss

Yes (vs. No or do not know)

0.95(0.80-1.12)

0.53

1.06(0.99-1.14)

0.098

1.05(0.98-1.12)

0.15

Frequency of toothache within the past 12 months (vs. Never)

Often

1.40(1.15-1.70)

0.0008

1.45(1.30-1.62)

<0.0001

1.44(1.31-1.59)

<0.0001

Occasionally

1.25(1.12-1.39)

<0.0001

1.28(1.21-1.36)

<0.0001

1.27(1.21-1.33)

<0.0001

Can't remember

1.09(0.95-1.25)

0.21

1.08(1.00-1.18)

0.063

1.08(1.00-1.16)

0.037

Time of last dental visit (vs. Never)

Within 6 months

1.23(1.07-1.43)

0.0047

1.43(1.33-1.52)

<0.0001

1.40(1.32-1.49)

<0.0001

Within 6 to 12 months

1.13(0.98-1.31)

0.095

1.25(1.17-1.34)

<0.0001

1.23(1.16-1.31)

<0.0001

More than 12 months

1.32(1.20-1.46)

<0.0001

1.17(1.10-1.24)

<0.0001

1.21(1.15-1.27)

<0.0001

Dental fluorosis

Yes (vs. No)

1.08(0.95-1.22)

0.25

0.95(0.89-1.01)

0.11

0.98(0.92-1.03)

0.37

Frequency of sweet snack intake (vs. Occasionally/ never)

Less than 2 times per week

0.92(0.81-1.05)

0.23

1.04(0.97-1.11)

0.29

1.00(0.93-1.07)

0.91

2 to 6 times per week

0.96(0.83-1.11)

0.58

1.09(1.02-1.17)

0.0073

1.03(0.96-1.10)

0.41

More than 6 times per week

0.93(0.82-1.04)

0.21

1.13(1.06-1.21)

<0.0001

1.06(0.99-1.13)

0.10

Year of survey

2015 (vs. 2005)

..

..

..

..

1.30(1.23-1.37)

<0.0001

Level-2 indicators

Economic development (vs. GDP per capita, quartile 1)

GDP per capita, , quartile 2

0.98(0.75-1.29)

0.90

1.08(0.86-1.35)

0.53

1.01(0.90-1.14)

0.85

GDP per capita, , quartile 3

1.21(0.90-1.62)

0.21

0.96(0.76-1.20)

0.71

0.96(0.86-1.08)

0.52

GDP per capita, , quartile 4

1.13(0.85-1.51)

0.40

1.10(0.87-1.38)

0.44

0.88(0.77-1.01)

0.068

Region (vs. East China)

North China

0.86(0.65-1.13)

0.27

0.93(0.73-1.19)

0.57

0.97(0.77-1.22)

0.80

Northeast China

1.15(0.84-1.57)

0.39

1.50(1.09-2.07)

0.014

1.35(1.03-1.77)

0.031

Middlesouth (Central) China

1.13(0.86-1.50)

0.38

1.18(0.92-1.52)

0.18

1.11(0.89-1.38)

0.37

Southwest China

1.27(0.91-1.78)

0.16

1.40(1.07-1.83)

0.013

1.26(0.99-1.59)

0.06

Northwest China

0.94(0.68-1.29)

0.69

1.05(0.79-1.39)

0.73

0.94(0.74-1.20)

0.64