Table 3 Negative binomial regression analyses of multimorbidity, IRR (95% CI)

 unpaved roads

 paved roads

0.88

(0.85–0.92) ^***

0.87

(0.83–0.91) ^***

0.86

(0.78–0.95) ^***

 others

0.93

(0.87–0.98) ^***

0.93

(0.87–0.99) ^**

0.90

(0.79–1.03)

Urban (vs. rural)

1.04

(1.01–1.08) ^*

1.05

(1.01–1.09) ^**

1.02

(0.95–1.10)

 0

 1

0.99

(0.95–1.03)

0.99

(0.95–1.03)

1.01

(0.92–1.11)

 2

0.99

(0.94–1.04)

1.00

(0.95–1.05)

1.02

(0.92–1.13)

 ≥ 3

0.90

(0.85–0.96) ^**

0.94

(0.89–0.99) ^*

0.94

(0.83–1.06)

Groundwater system (yes vs. no)

1.00

(0.96–1.04)

1.00

(0.96–1.05)

1.02

(0.94–1.11)

Age

1.00

(0.98–1.01)

1.00

(1.00–1.00)

1.00

(1.00–1.00)

Women (vs. men)

1.00

(0.96–1.03)

1.00

(0.96–1.04)

0.99

(0.96–1.03)

Married (vs. others)

0.97

(0.93–1.02)

0.97

(0.93–1.01)

0.97

(0.93–1.02)

 1st (the poorest)

 2nd

1.03

(0.98–1.07)

1.03

(0.98–1.08)

0.99

(0.95–1.04)

 3rd

0.96

(0.91–1.00)

0.95

(0.93–1.00)

0.94

(0.89–0.99) ^*

 4th (the richest)

0.94

(0.89–0.99) ^*

0.93

(0.89–0.98) ^**

0.93

(0.88–0.98) ^*

 illiteracy

 some primary school

1.03

(0.97–1.08)

1.03

(0.97–1.08)

1.03

(0.98–1.08)

 primary school

1.01

(0.96–1.06)

1.01

(0.96–1.06)

1.00

(0.95–1.06)

 junior school or above

1.03

(0.99–1.07)

1.03

(0.98–1.08)

1.02

(0.97–1.08)

 uninsured

 RCMI

1.03

(0.96–1.10)

1.03

(0.96–1.11)

1.04

(0.97–1.11)

 others

1.04

(0.96–1.12)

1.06

(0.98–1.15)

1.07

(0.99–1.15)

 < 18.5

 ≥ 18.5 and < 25

0.91

(0.85–0.97) ^*

0.91

(0.85–0.97) ^**

0.90

(0.84–0.96) ^**

 ≥ 25 and < 30

1.15

(1.08–1.24) ^***

1.16

(1.08–1.25) ^***

1.14

(1.06–1.22) ^***

 ≥ 30

1.36

(1.24–1.50) ^***

1.37

(1.24–1.50) ^***

1.33

(1.21–1.46) ^***

Physical activity

 never

 seldom

1.00

(0.83–1.21)

1.00

(0.83–1.20)

0.96

(0.80–1.15)

 a weekly basis

1.09

(0.92–1.29)

1.09

(0.92–1.29)

1.06

(0.90–1.25)

 a daily basis

1.10

(1.01–1.20) ^*

1.08

(0.99–1.18)

1.08

(0.98–1.18)