. Author manuscript; available in PMC: 2015 Aug 4.

Published in final edited form as: J Occup Environ Med. 2013 Jul;55(7):846–850. doi: 10.1097/JOM.0b013e31828dc985

TABLE 5.

Results From Cox Proportional Hazards Models of Abnormal Spirometry Results^a

	Model 1 (All Variables, Including Both CWP, PMF; n = 6372^b)		Model 2 (210 Simple CWP Excluded; n = 6162^b)		Model 3 (45 Miners With PMF Excluded; n = 6327^b)
Variable	Coefficient (SE)	Prevalence Ratio	Coefficient (SE)	Prevalence Ratio	Coefficient (SE)	Prevalence Ratio
Age, y	0.018 (0.004)	1.02^***	0.018 (0.004)	1.02^***	0.018 (0.004)	1.02^***
BMI, kg/m²	0.046 (0.006)	1.05^***	0.047 (0.006)	1.05^***	0.046 (0.006)	1.05^***
Tenure underground, y	−0.0002 (0.003)	1.00	−0.0001 (0.003)	1.00	−0.0005 (0.003)	1.00
Current smoker (1, 0)	0.808 (0.074)	2.24^***	0.809 (0.076)	2.25^***	0.821 (0.074)	2.27^***
PMF (1, 0)	0.724 (0.273)	2.06^*	1.309 (0.240)	3.70^***	NA	NA
CWP (1, 0)	0.583 (0.143)	1.79^***	NA	NA	0.582 (0.143)	1.79^***

P < 0.01;

^***

P < 0.0001.

Model 1—full model, independent variables for both CWP and PMF. Model 2—210 simple CWP not included in the model. Model 3—excluding 45 cases of PMF.

One subject missing underground tenure.

BMI, body mass index; CWP, coal workers' pneumoconiosis; NA, not applicable; PMF, progressive massive fibrosis; y, years.