Characteristics of volunteers and matched controls
| Characteristic | Total | Smelter Plant 1 | Smelter Plant 2 | Fabrication Plant | ||||||||||||||||
| Quiet dose volunteers (n=110) | Controls (n=110) | P value | Quiet dose volunteers (n=11) | Controls (n=11) | P value | Quiet dose volunteers (n=57) | Controls (n=57) | P value | Quiet dose volunteers (n=42) | Controls (n=42) | P value | |||||||||
| Age—(years) mean, SD | 44.2 | 10.2 | 44.0 | 10.0 | 0.8568 | 46.6 | 6.7 | 46.0 | 6.4 | 0.8217 | 41.4 | 10.5 | 41.5 | 10.4 | 0.9929 | 47.4 | 9.6 | 46.9 | 9.3 | 0.8092 |
| Male—n, % | 83 | 75.5 | 83 | 75.5 | 1.0000 | 11 | 100.0 | 11 | 100.0 | 1.0000 | 49 | 86.0 | 49 | 86.0 | 1.0000 | 23 | 54.8 | 23 | 54.8 | 1.0000 |
| Race—n, % | 1.0000 | 1.0000 | 1.0000 | 1.0000 | ||||||||||||||||
| White | 107 | 97.3 | 107 | 97.3 | 10 | 90.9 | 10 | 90.9 | 56 | 98.2 | 56 | 98.2 | 41 | 97.6 | 41 | 97.6 | ||||
| Black | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 | ||||
| Other | 3 | 2.7 | 3 | 2.7 | 1 | 9.1 | 1 | 9.1 | 1 | 1.8 | 1 | 1.8 | 1 | 2.4 | 1 | 2.4 | ||||
| Tinnitus—n, % | 20 | 18.2 | 31 | 28.2 | 0.0788 | 4 | 36.4 | 2 | 18.2 | 0.3384 | 10 | 17.5 | 24 | 42.1 | 0.0042 | 6 | 14.3 | 5 | 11.9 | 0.7464 |
| Noisy hobbies—n, % | 52 | 47.3 | 62 | 56.4 | 0.1772 | 5 | 45.5 | 6 | 54.5 | 0.6698 | 33 | 57.9 | 40 | 70.2 | 0.1719 | 14 | 33.3 | 16 | 38.1 | 0.6488 |
| Shoot or hunt—n, % | 45 | 40.9 | 60 | 54.5 | 0.0429 | 6 | 54.5 | 5 | 45.5 | 0.6698 | 30 | 52.6 | 33 | 57.9 | 0.572 | 9 | 21.4 | 22 | 52.4 | 0.0033 |
| Current other noisy job—n, % | 4 | 3.6 | 22 | 20.0 | 0.0002 | 0 | 0.0 | 2 | 18.2 | 0.138 | 2 | 3.5 | 20 | 35.1 | <0.0001 | 2 | 4.8 | 0 | 0.0 | 0.1523 |
| Previous loud job—n, % | 67 | 60.9 | 87 | 79.1 | 0.0033 | 6 | 54.5 | 5 | 45.5 | 0.6698 | 44 | 77.2 | 44 | 77.2 | 1.0000 | 17 | 40.5 | 38 | 90.5 | <0.0001 |
| Estimated ambient noise (dBA)—mean, SD | 83.8 | 5.2 | 83.9 | 5.2 | 0.9170 | 81.6 | 2.2 | 81.6 | 2.2 | 1.0000 | 80.4 | 3.9 | 80.5 | 4.0 | 0.862 | 89.1 | 1.8 | 89.1 | 1.8 | 0.9674 |
| Binaural hearing threshold level at start*—mean, SD | 17.5 | 12.1 | 16.0 | 11.1 | 0.3320 | 22.2 | 13.0 | 21.1 | 13.2 | 0.841 | 15.1 | 11.5 | 14.7 | 9.6 | 0.8425 | 19.5 | 12.1 | 16.3 | 12.4 | 0.2413 |
| Years between audiograms—mean, SD | 4.4 | 1.3 | 4.6 | 1.5 | 0.2497 | 5.4 | 1.4 | 4.9 | 1.2 | 0.3225 | 5.1 | 1.1 | 5.4 | 1.0 | 0.0822 | 3.3 | 0.4 | 3.5 | 1.3 | 0.2704 |
| Annual rate of hearing loss*— (dB/year)—mean, SD | 0.66 | 1.44 | 0.37 | 1.19 | 0.1085 | 1.55 | 1.18 | 0.06 | 1.00 | 0.0047 | 0.61 | 1.08 | 0.35 | 0.94 | 0.1671 | 0.49 | 1.82 | 0.49 | 1.50 | 0.9924 |
*Binaural average of 3, 4, 6 kHz.