Table 1.

Unadjusted prevalence of airflow obstruction and moderate/severe airflow obstruction among never-smoking coal miners

	No. sample (n=5316)	Prevalence of airflow obstruction (n=410)	Prevalence of moderate/severe airflow obstruction (n=57)
Characteristics		percent	percent
Total		7.7	1.1
No coal workers’ pneumoconiosis (category 0)	5200	7.5*	1.0*
All coal workers’ pneumoconiosis	116	16.4	3.5
Simple coal workers’ pneumoconiosis	85	10.6	1.2
Category 1	67	10.5	1.5
Categories 2–3	18	11.1	0.0
Progressive massive fibrosis	31	32.3*	9.7*
Age group (years)
<40	1645	8.4*	0.6
40–49	1247	7.5	1.0
50–59	1968	6.7	1.4
≥60	456	10.3	1.5
Sex
Male	5159	7.8	1.1
Female	157	5.1	1.3
Race
White	4874	7.8	1.1
Other	442	7.0	0.7
Surface only miners	982	6.6	1.2
Underground only miners	3437	8.2	1.1
Both surface & underground miners	810	6.9	0.7
Surface mining tenure (years)	Mean=13.1
1–<10	965	7.2	0.9
10–25	428	5.6	0.9
≥25	399	7.0	1.3
Underground mining tenure (years)	Mean=18.9
1–<10	1351	8.5	0.6
10–25	1152	7.2	1.1
≥25	1744	8.0	1.3
Total mining tenure (years)	Mean=19.8
1–<10	1606	8.3	0.8
10–25	1292	7.0	1.2
≥25	2331	7.7	1.2

Miner type and mining tenure data were missing for 87 miners.

^*Indicates significant p value (<0.05) based on χ² or Fisher exact test.