Table 1.

Demographic characteristics of the study and control populations at the baseline

Characteristic	Total		With		Without		P-valuea
	n	%	n	%	n	%
Total	46,865		9373	20.00	37,492	80.00
Age (years)	42.08 ± 16.59		42.06 ± 16.09		42.09 ± 16.71		0.889
Age group (years)							0.999
18–44	28,350	60.49	5670	60.49	22,680	60.49
45–64	13,615	29.05	2723	29.05	10,892	29.05
≥ 65	4900	10.46	980	10.46	3920	10.46
Insured premium (NT$)							<0.001
< 18,000	42,248	90.15	9198	98.13	33,050	88.15
18,000–34,999	3221	6.87	154	1.64	3067	8.18
≥ 35,000	1396	2.98	21	0.22	1375	3.67
CCI	0.48 ± 1.40		0.61 ± 1.46		0.45 ± 1.39		<0.001
Season							<0.001
Spring (March-May)	12,194	26.02	2380	25.39	9814	26.18
Summer (June-August)	11,466	24.47	2485	26.51	8981	23.95
Autumn (September-November)	11,242	23.99	2212	23.60	9030	24.09
Winter (December-February)	11,963	25.53	2296	24.50	9667	25.78
Location							<0.001
Northern Taiwan	18,550	39.58	3241	34.58	15,309	40.83
Middle Taiwan	13,405	28.60	2478	26.44	10,927	29.14
Southern Taiwan	11,774	25.12	2331	24.87	9443	25.19
Eastern Taiwan	2947	6.29	1316	14.04	1631	4.35
Outlets islands	189	0.40	7	0.07	182	0.49
Urbanization level							<0.001
1 (The highest)	16,142	34.44	2345	25.02	13,797	36.80
2	20,160	43.02	4746	50.63	15,414	41.11
3	3815	8.14	630	6.72	3185	8.50
4 (The lowest)	6748	14.40	1652	17.63	5096	13.59
Level of care							<0.001
Hospital center	14,329	30.58	2863	30.55	11,466	30.58
Regional hospital	15,771	33.65	4676	49.89	11,095	29.59
Local hospital	16,765	35.77	1834	19.57	14,931	39.82

^aChi-square/Fisher’s exact test on categorical variables and t-test on continuous variables

Abbreviation: CCI, Charlson comorbidity index