Table 4 Incidence risk ratio (IRR) and 95 % confidence interval (CI) of outpatient care utilization with four types of status of public and private health insurance in the Korea Health Panel Survey, 2008–2011

Gender (Ref.: Men)

1

1

1

1

 Women

1.58***

1.53–1.63

1.52***

1.47–1.57

1.52***

1.47–1.57

1.52***

1.48–1.57

Age (Ref.: 20–29)

1

1

1

1

 30–39

1.09***

1.05–1.13

1.05**

1.01–1.09

1.04*

1.01–1.09

1.05*

1.01–1.09

 40–49

1.29***

1.24–1.35

1.20***

1.15–1.25

1.19***

1.14–1.24

1.19***

1.14–1.24

 50–59

1.73***

1.65–1.81

1.52***

1.45–1.59

1.51***

1.44–1.58

1.51***

1.44–1.58

 60 or older

2.40***

2.29–2.51

2.04***

1.94–2.14

2.03***

1.93–2.13

2.03***

1.93–2.13

Chronic disease (Ref.: No)

1

1

1

1

 Yes

1.98***

1.96–2.01

1.97***

1.94–2.00

1.97***

1.94–1.99

1.97***

1.94–1.99

Marital status (Ref.: Single)

1

1

1

1

 Married couple

1.73***

1.66–1.81

1.67***

1.60–1.75

1.69***

1.61–1.79

1.69***

1.61–1.76

 Divorced or Separated

1.95***

1.84–2.07

1.86***

1.75–1.98

1.85***

1.74–1.97

1.85***

1.74–1.97

 Separation by death

1.92***

1.82–2.02

1.76***

1.70–1.89

1.79***

1.70–1.89

1.79***

1.70–1.89

Education (Ref.: College Degree or higher)

1

1

1

 High School to associate

1.16***

1.12–1.21

1.15***

1.11–1.19

1.15***

1.11–1.19

 Middle School to associate

1.34***

1.28–1.41

1.33***

1.27–1.39

1.33***

1.27–1.39

 Elementary School or less

1.55***

1.48–1.63

1.53***

1.46–1.60

1.53***

1.46–1.60

Household income (Ref.: 1^st quartile, lowest)

1

1

1

1

 2^st quartile

0.98**

0.97–0.99

0.98**

0.97–0.99

0.98**

0.97–0.99

 3^st quartile

0.99**

0.97–0.99

0.99

0.98–1.00

0.99

0.98–1.00

 4^st quartile (highest)

0.99

0.98–1.00

0.99

0.98–1.00

0.99

0.98–1.00

Healthcare covered by NHI (Ref.: Yes)

1

 No (medical aid)

1.23***

1.20–1.26

Purchase of PHI (Ref.: No)

1

 Yes

1.02

0.99–1.03

NHI status x PHI status (Ref.: Covered by only NHI)

1

 Covered by only the medical aid

1.23***

1.19–1.26

 Covered by both NHI and PHI

1.01

0.99–1.03

 Covered by both the medical aid and PHI

1.25***

1.21–1.29