Table 3. Factors of joint replacement surgery by using Cox regression.

Variables	Crude HR	95% CI Lower limit	95% CI Upper limit	P	Adjusted HR	95% CI Lower limit	95% CI Upper limit	P
Metformin
Without	Reference				Reference
With	0.781	0.634	0.962	0.020	0.742	0.601	0.915	0.005
MPR of metformin
Without	Reference
<40%	0.885	0.629	1.162	0.316
40–80%	0.797	0.598	1.061	0.120
>80%	0.634	0.412	0.977	0.039
Gender
Male	0.850	0.701	1.029	0.095	0.920	0.757	1.117	0.399
Female	Reference				Reference
Age (years)	0.969	0.962	0.977	<0.001	0.971	0.964	0.979	<0.001
CCI removed DM	0.612	0.544	0.688	<0.001	0.647	0.578	0.725	<0.001
Location					Had collinearity with urbanization level
Northern Taiwan	Reference
Middle Taiwan	0.613	0.484	0.775	<0.001
Southern Taiwan	0.705	0.555	0.895	0.004
Eastern Taiwan	0.628	0.429	0.918	0.016
Outlets islands	0.817	0.303	2.200	0.689
Urbanization level
1 (The highest)	1.773	1.452	2.457	0.006	1.734	1.401	2.001	0.013
2	1.245	1.126	2.118	0.012	1.201	1.096	1.978	0.027
3 (The lowest)	Reference				Reference
Level of care
Hospital center	1.995	1.554	2.561	<0.001	1.673	1.265	2.214	<0.001
Regional hospital	1.258	0.978	1.618	0.074	1.113	0.862	1.437	0.410
Local hospital	Reference				Reference
Insured premium (NT$)
<10,000	Reference				Reference
10,000–14,999	1.459	0.875	3.742	0.305	1.269	0.855	3.307	0.256
≧15,000	1.546	0.903	3.886	0.496	1.334	0.894	3.521	0.452

HR = hazard ratio; CI = confidence interval; Adjusted HR: Adjusted variables listed in the table