Effect of Workplace Noise on Hearing Ability in Tile and Ceramic Industry Workers in Iran: A 2-Year Follow-Up Study

Table 3

Prevalence of mean threshold change at 3000, 4000, and 6000 Hz in each job category.

Job category	Follow-up year	Threshold change
		Negative		Positive
		Number	Percent	Number	Percent
Control	1st	108	96.43	4	3.57
	2nd	110	98.21	2	1.79
1	1st	181	91.88	16	8.12
	2nd	148	75.13	49	24.87
2	1st	129	89.58	15	10.42
	2nd	93	64.57	51	35.43
3	1st	96	94.12	6	5.88
	2nd	87	85.29	15	14.71