Results from regression analysis of classification 0/1+ small opacities for men
| Respirable fibres (f.ml−1.y) | Duration in production (y) | |
| Up to 1971 (per 1 unit) | 1.54 (0.81 to 2.96) | 1.31 (0.90 to 1.90) |
| 1972–76 (per 1 unit) | 1.06 (0.83 to 1.34) | 1.16 (0.95 to 1.41) |
| 1977–81 (per 1 unit) | 1.03 (0.90 to 1.17) | 1.05 (0.95 to 1.16) |
| 1982–86 (per 1 unit) | 1.06 (0.95 to 1.18) | 1.05 (0.97 to 1.14) |
| 1987–91 (per 1 unit) | 1.13 (1.00 to 1.29) | 1.09 (1.01 to 1.17) |
| 1992–96 (per 1 unit) | 1.28 (1.05 to 1.55) | 1.11 (1.03 to 1.20) |
9-150 ORs (95% CIs) are calculated from model also containing terms for age, smoking, and amount smoked. Each period fitted in a separate regression model.