Association between Coalmine Dust and Mortality Risk of Lung Cancer: A Meta-Analysis

Table 3

Results of subgroup analyses for the selected studies.

Prespecified or not	Groups	Subgroups	No. of studies	No. of events	Outcome with 95% CI	value for outcome	(%)	value for heterogeneity
Yes	Outcome type	SMR	15	3355	1.13 (0.95-1.35)	0.154	95.3	<0.001
		PMR	3	5492	0.99 (0.82-1.20)	0.901	94.2	<0.001
		OR	2	NA	1.64 (0.46-5.82)	0.442	92.0	<0.001
		RR	2	62	2.12 (0.76-5.88)	0.149	88.6	0.003
Yes	Ethnicity	Asian	3	97	4.94 (3.95-6.17)	<0.001	39.3	0.192
		Caucasian	15	7824	1.05 (0.94-1.17)	0.402	92.4	<0.001
		Caucasian/Negro	4	988	0.96 (0.82-1.12)	0.595	72.3	0.013
No	Control group	General population	17	8574	1.23 (1.08-1.40)	0.002	95.5	<0.001
		Coalminers	3	65	1.19 (0.66-2.15)	0.558	87.8	<0.001
		Quarrymen	2	270	0.78 (0.60-1.02)	0.066	67.7	0.078
No	Case group	Coalminers with pneumoconiosis	3	449	2.11 (0.89-5.03)	0.091	98.6	<0.001
		Coalminers	19	8460	1.04 (0.94-1.14)	0.472	90.8	<0.001
Yes	Type of research	Cohort study	8	2299	1.42 (1.10-1.85)	0.008	96.8	<0.001
		Case control study	3	272	1.26 (0.81-1.96)	0.312	84.5	0.002
		Descriptive study	11	6338	1.01 (0.87-1.17)	0.933	92.9	<0.001
No	Observed deaths	<100	9	339	1.28 (0.74-2.22)	0.376	95.5	<0.001
		>100	13	8570	1.10 (0.99-1.22)	0.086	94.0	<0.001
No	Year of publication	1964-1980	9	1723	0.99 (0.80-1.23)	0.935	92.3	<0.001
		1980-2000	8	5070	1.56 (1.10-2.20)	0.012	96.9	<0.001
		2000-2017	5	2116	1.09 (0.94-1.26)	0.247	89.4	<0.001
No	Area	China	3	97	4.94 (3.95-6.17)	<0.001	39.3	0.192
		UK	7	6750	0.92 (0.82-1.03)	0.137	89.4	<0.001
		US	9	1531	1.09 (0.92-1.29)	0.338	87.3	<0.001
		Others	3	531	1.13 (0.79-1.61)	0.521	94.1	<0.001
No	Duration of follow-up (years)	<10	10	6330	1.26 (1.00-1.56)	0.048	97.2	<0.001
		>10 and <20	5	492	1.08 (0.80-1.47)	0.607	85.2	<0.001
		>20	7	2087	1.10 (0.96-1.26)	0.172	84.8	<0.001
No	Study quality	Moderate	8	5964	1.01 (0.84-1.22)	0.908	94.8	<0.001
		High	14	2945	1.28 (1.07-1.53)	0.006	94.4	<0.001

Abbreviation: OR: odds ratio; PMR: proportional mortality ratio; RR: relative risk; SMR: standardized mortality ratio; 95% CI: 95% confidence interval.