Table 2. Distribution of characteristics among study population stratified by risk levels.

Variables		Risk Levels								p-value*
		Control (n=200)			Risk Level 1 (n=139)			Risk Level 2 (n=119)
		n	(%)		n	(%)		n	(%)
Age
	≤40	135	67.5		101	72.7		93	78.2	0.12
	>40	65	32.5		38	27.3		26	21.9
Gender
	Female	80	40.0		35	25.2		26	21.9	<0.01
	Male	120	60.0		104	74.8		93	78.2
Ethnicity
	Taiwanese	157	79.3		109	78.4		92	77.3	0.55
	Hakka	22	11.1		15	10.8		19	16.0
	Mainlander and Aborigine	19	9.6		15	10.8		8	6.7
Education
	High school and less	38	19.2		18	13.1		20	16.8	0.03
	University	104	52.5		62	45.3		47	39.5
	Graduate school	56	28.3		57	41.6		52	43.7
Smoking
	No	174	87.9		118	85.5		97	81.5	0.30
	Yes	24	12.1		20	14.5		22	18.5
Alcohol drinking
	No	180	90.5		133	95.7		103	86.6	0.04
	Yes	19	9.6		6	4.3		16	13.5
Betel nut chewing
	No	196	98.5		139	100.0		112	94.1	<0.01
	Yes	3	1.5		0	0.0		7	5.9

*p value for χ² test