Table 2.

Cardiovascular and hearing conditions of the two exposure groups.

Variable		All (N = 5205)		High exposure level (N = 1041)		Low exposure level (N = 4164)		P a
		n	%	n	%	n	%
Hypertension	Without	4589	88.17	899	86.36	3690	88.62	0.047
	With	616	11.83	142	13.64	474	11.38
ECG	Normal	4518	86.80	898	86.26	3620	86.94	0.573
	Abnormal	687	13.20	143	13.74	544	13.06
Hearing Loss	Without	4048	77.77	773	74.26	3275	78.65	0.003
	With	1157	22.23	268	25.74	889	21.35

^aTwo-sided χ² test for the frequency distributions of selected variables between low and high exposure level.