Table 4.
Proportional hazard ratios on underlying cause lung cancer mortality for 15-year lagged REC cumulative exposure and average intensity for ever-underground workers: quartiles, expanded categories, and continuous modeling results*
| Analyses | Results for quartiles, expanded categories, and continuous models for ever-underground workers | |||||||
| Quartiles (122 LC deaths) | ||||||||
| Cumulative REC exposure (μg/m3-y) | ||||||||
| Exposure range | 0 to <108 | 108 to <445 | 445 to <946 | ≥946 | ||||
| No. LC deaths | 30 | 31 | 30 | 31 | ||||
| REC HR (95% CI) | 1.00 (referent) | 1.50 (0.86 to 2.62) | 2.17 (1.21 to 3.88) | 2.21 (1.19 to 4.09) | ||||
| P | .152 | .009 | .012 | |||||
| Average REC intensity (μg/m3) | ||||||||
| Exposure range | 0 to <11 | 11 to <51 | 51 to <111 | ≥111 | ||||
| No. LC deaths | 30 | 31 | 30 | 31 | ||||
| REC HR (95% CI) | 1.00 (referent) | 1.73 (0.99 to 3.05) | 2.11 (1.14 to 3.90) | 1.86 (0.98 to 3.52) | ||||
| P | .056 | .018 | .057 | |||||
| Expanded categories (excluding <5 year tenure, 93 LC deaths) | ||||||||
| Cumulative REC exposure (μg/m3-y) | ||||||||
| Exposure range | 0 to <20 | 20 to <40 | 40 to <80 | 80 to <160 | 160 to <320 | 320 to <640 | 640 to <1280 | ≥1280 |
| No. LC deaths | 8 | 3 | 2 | 10 | 12 | 14 | 30 | 14 |
| REC HR (95% CI) | 1.00 (referent) | 1.39 (0.36 to 5.39) | 0.82 (0.17 to 4.03) | 2.69 (0.99 to 7.37) | 2.67 (0.98 to 7.27) | 2.21 (0.82 to 5.97) | 5.01 (1.97 to 12.76) | 2.39 (0.82 to 6.94) |
| P | .634 | .807 | .054 | .055 | .119 | .001 | .109 | |
| Average REC intensity (μg/m3) | ||||||||
| Exposure range | 0 to <2 | 2 to <4 | 4 to <8 | 8 to <16 | 16 to <32 | 32 to <64 | 64 to <128 | ≥128 |
| No. LC deaths | 9 | 2 | 5 | 8 | 8 | 27 | 14 | 20 |
| REC HR (95% CI) | 1.00 (referent) | 0.93 (0.19 to 4.49) | 1.00 (0.31 to 3.18) | 1.79 (0.65 to 4.92) | 2.01 (0.74 to 5.50) | 3.20 (1.36 to 7.51) | 2.11 (0.81 to 5.48) | 3.04 (1.20 to 7.71) |
| P | .930 | .998 | .261 | .173 | .008 | .125 | .019 | |
| Continuous models (excluding <5 y tenure) | ||||||||
| Cumulative REC exposure | ||||||||
| Exposure range | Full | Full | <1280 μg/m3-y | |||||
| Exposure units | 1000 μg/m3-y | Log μg/m3-y | 1000 μg/m3-y | |||||
| No. LC deaths | 93 | 93 | 79 | |||||
| REC HR (95% CI) | 1.07 (0.85 to 1.35) | 1.19 (1.04 to 1.37) | 4.06 (2.11 to 7.83) | |||||
| P | .585 | .015 | <.001 | |||||
| Average REC intensity | ||||||||
| Exposure range | Full | Full | ||||||
| Exposure units | 100 μg/m3 | Log μg/m3 | ||||||
| No. LC deaths | 93 | 93 | ||||||
| REC HR (95% CI) | 1.25 (0.93 to 1.68) | 1.26 (1.06 to 1.50) | ||||||
| P | .138 | .010 | ||||||
*
CI = confidence interval; HR = hazard ratio; LC = lung cancer; REC = respirable elemental carbon; P = HR probability from two-sided χ2 Wald test. Workers categorized as ever-underground after first going underground (even if surface later). Models adjusted for race/ethnicity and birth year; stratified by state. Race/ethnicity was unstable in model with restricted cumulative REC exposure range and was omitted. Inclusion of the variable had little impact.