Characteristics of intervention subjects and controls
| Characteristic | Intervention subjects (N=78) | Workers in seven other smelters (N=2210) | Matched controls (N=234) |
| Age (mean, SD) | 48.7 (7.2) | 46.7 (8.2) | 48.6 (7.5) |
| Male (n, %) | 78 (100.0) | 2045 (92.5) | 234 (100.0) |
| Race (n, %) | |||
| White | 69 (88.5) | 1873 (84.8) | 224 (95.7) |
| Hispanic | 6 (7.7) | 37 (1.7) | 5 (2.1) |
| American Indian/Alaska native | 2 (2.6) | 20 (0.9) | 2 (1.0) |
| Asian | 1 (1.3) | 6 (0.3) | 0 (0.0) |
| African American | 0 (0.0) | 274 (12.4) | 3 (1.3) |
| Tenure (mean, SD) | 22.5 (9.9) | 18.5 (10.5) | 20.6 (10.4) |
| History of shooting (n, %) | 30 (38.5) | 904 (40.9) | 113 (48.3) |
| Hearing at start of intervention (mean, SD) | |||
| Average 2–4 KHz | 28.2 (13.4) | 20.5 (15.1) | 28.2 (13.6) |