Table 4 Follow up of hearing level (dB) at the average of 2, 3 and 4 kHz across the four study periods stratified by work duration in years

≤ 10

0.257

Firefighter

13.11 ± 10.69

13.74 ± 11.10

13.53 ± 11.57

12.75 ± 11.92

Factory worker

24.72 ± 13.47

22.50 ± 15.07

20.83 ± 15.21

23.33 ± 15.43

10 - ≤ 20

< 0.0001

Firefighter

16.56 ± 11.67

17.31 ± 12.44

17.57 ± 13.01

17.28 ± 13.06

Factory worker

29.07 ± 13.44

28.10 ± 12.93

26.76 ± 13.72

28.57 ± 14.80

> 20

0.001

Firefighter

21.80 ± 13.22

24.72 ± 13.61

24.85 ± 13.44

25.27 ± 13.52

Factory worker

33.76 ± 12.06

34.85 ± 12.97

33.24 ± 12.76

35.17 ± 13.50