Working years | N | Speech frequency | 3 kHz | 4 kHz | 6 kHz | 3 kHz + 4 kHz | 3 kHz + 6 kHz | 4 kHz + 6 kHz | 3 kHz + 4 kHz + 6 kHz |
3 - 5 | 38 | 29.78 ± 9.83 | 31.70 ± 9.78 | 32.28 ± 9.42 | 32.32 ± 9.58 | 32.03 ± 9.58 | 32.07 ± 9.63 | 32.33 ± 9.48 | 32.12 ± 9.55 |
6 - 10 | 67 | 30.49 ± 9.28 | 32.31 ± 9.17 | 32.72 ± 8.53 | 33.39 ± 8.66 | 32.56 ± 8.83 | 32.90 ± 8.85 | 33.09 ± 8.57 | 32.83 ± 8.72 |
>10 | 63 | 31.90 ± 13.55 | 33.99 ± 13.04 | 34.47 ± 12.59 | 34.73 ± 12.99 | 34.26 ± 12.81 | 34.40 ± 12.98 | 34.74 ± 12.77 | 34.40 ± 12.85 |
Total | 168 | 30.74 ± 11.24 | 32.70 ± 10.98 | 33.20 ± 10.54* | 33.46 ± 10.80* | 32.98 ± 10.75 | 33.13 ± 10.84* | 33.57 ± 10.65* | 33.14 ± 10.74* |