Table 5.

Proportional hazard ratios on underlying cause lung cancer mortality for 15-year lagged REC cumulative exposure and average intensity for surface-only workers: quartiles, expanded categories, and continuous modeling results^*

Analyses	Results for quartiles, expanded categories, and continuous models for surface-only workers
Quartiles (78 LC deaths)
Cumulative REC exposure (μg/m3-y)
Exposure range	0 to <0.70	0.70 to <4.6	4.6 to <14	≥14
No. LC deaths	19	20	19	20
REC HR (95% CI)	1.00 (referent)	1.28 (0.64 to 2.58)	0.73 (0.35 to 1.53)	1.00 (0.44 to 2.28)
P		.490	.407	.998
Average REC intensity (μg/m3)
Exposure range	0 to <0.57	0.57 to <0.91	0.91 to <1.4	≥1.4
No. LC deaths	19	18	21	20
REC HR (95% CI)	1.00 (referent)	1.71 (0.82 to 3.58)	2.22 (1.01 to 4.90)	2.56 (1.09 to 6.03)
P		.154	.049	.031
Expanded categories (excluding <5 year tenure, 57 LC deaths)
Cumulative REC exposure (μg/m3-y)
Exposure range	0 to <20	20 to <40	40 to <80	≥80
No. LC deaths	44	7	4	2
REC HR (95% CI)	1.00 (referent)	1.16 (0.46 to 2.94)	2.29 (0.60 to 8.75)	8.68 (1.61 to 46.90)
P		.756	.224	.012
Average REC intensity (μg/m3)
Exposure range	0 to <2	2 to <4	≥4
No. LC deaths	44	11	2
REC HR (95% CI)	1.00 (referent)	2.33 (1.11 to 4.90)	4.63 (0.99 to 21.55)
P		.026	.051
Continuous models (excluding <5 y tenure)
Cumulative REC exposure
Exposure range	Full		Full
Exposure units	μg/m3-y		Log μg/m3-y
No. LC deaths	57		57
REC HR (95% CI)	1.02 (1.00 to 1.03)		1.03 (0.75 to 1.42)
P	.026		.842
Average REC intensity
Exposure range	Full		Full
Exposure units	μg/m3		Log μg/m3
No. LC deaths	57		57
REC HR (95% CI)	1.42 (1.10 to 1.82)		2.60 (1.07 to 6.29)
P	.006		.034

^*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 surface-only until first going underground (if ever). Models adjusted for race/ethnicity, birth year, and sex; stratified by state.