Demographic and mining characteristics of cases by type of PMF
| Coal type | Mixed type | Silica type | P value | |
| n | 138 | 129 | 55 | |
| White (n, %) | 118 (86.1) | 117 (90.7) | 49 (89.1) | NS |
| Age at death (years) (mean, SD) | 70.8 (8.6) | 72.2 (8.5) | 70.1 (10.6) | NS |
| Year of birth (mean, SD) | 1912 (11) | 1914 (10) | 1917 (15) | 0.025 |
| Year of death (mean, SD) | 1984 (8) | 1986 (9) | 1988 (10.4) | 0.005 |
| Coal mine experience (n, %) | NS | |||
| Underground only | 111 (83.5) | 107 (83.4) | 41 (75.9) | |
| Underground and surface | 22 (16.5) | 21 (16.4) | 13 (24.1) | |
| Total years of coal mining (mean, SD) | 36.4 (8.5) | 36.7 (9.4) | 34.9 (10.3) | NS |
| Years of underground coal mining | 35.1 (9.3) | 35.1 (10.8) | 31.6 (12.4) | NS |
| Years of surface coal mining | 1.3 (4.8) | 1.6 (6.1) | 3.3 (7.8) | NS |
| Work in central Appalachia | 60 (43.5%) | 40 (31.0%) | 22 (17.1%) | NS |
NS, not significant; PMF, progressive massive fibrosis.