Table 1.

Characteristics of nasopharyngeal carcinoma (NPC) cases and controls

Characteristics	Cases (n=2528)		Controls (n=2596)		P value
	No.	%	No.	%
Residential area					0.28
Zhaoqing	1283	50.8	1321	50.9
Wuzhou	688	27.2	664	25.6
Guiping/Pingnan	557	22.0	611	23.5
Sex					1.00
Male	1858	73.5	1908	73.5
Female	670	26.5	688	26.5
Age at diagnosis/referral (years)
Mean (SD)	48.6 (10.6)		49.8 (10.9)		<0.001*
20–29	82	3.3	80	3.1	0.007
30–39	423	16.7	372	14.3
40–49	910	36.0	890	34.3
50–59	686	27.1	729	28.1
60–74	427	16.9	525	20.2
Education level (years)					0.003
≤ 6	1005	39.8	932	35.9
7– 9	1013	40.1	1040	40.1
10–12	403	15.9	483	18.6
> 12	107	4.2	141	5.4
Current housing type					<0.001
Building (concrete structure)	1818	71.9	2019	77.8
Cottage (clay brick structure)	700	27.7	574	22.1
Boat	10	0.4	2	0.1
Missing			1
Current occupation					<0.001
Unemployed	77	3.1	95	3.7
Farmer	855	33.8	984	37.9
Blue-collar	1020	40.4	900	34.7
White-collar	350	13.8	416	16.0
Other/unknown	226	8.9	201	7.7
First-degree family history of NPC					<0.001
No	2204	87.2	2482	95.6
Yes	272	10.8	70	2.7
Unknown	46	1.8	43	1.7
Missing	6	0.2	1	0.04
Cigarette smoking					0.07
Never	1117	44.2	1213	46.7
Ever	1410	55.8	1381	53.2
Missing	1	0.04	2	0.1
Tea drinking					<0.001
Less than daily	1614	63.8	1512	58.2
Daily	911	36.1	1081	41.6
Missing	3	0.1	3	0.1
Salt-preserved fish consumption in 2000–2002					0.02
Yearly or less	1853	73.3	1901	73.2
Monthly	484	19.2	542	20.9
Weekly or more	188	7.4	149	5.7
Missing	3	0.1	4	0.2

SD = standard deviation.

^*P value was determined by a two-sided t-test. Other P values were determined by a chi-square test.