Evidence relating cigarette, cigar and pipe smoking to lung cancer and chronic obstructive pulmonary disease: Meta-analysis of recent data from three regions

Table 4 Chronic obstructive pulmonary disease and current vs never cigarette smoking – results from random effects meta-analyses

Full output table	Factor	Level	No. of RRs	No. of Studies	RR (95%CI)	Heterogeneity test by level (NS = P ≥ 0.1) and trend if relevant
	All		23	18	9.19 (6.97-12.13)	P < 0.001
4	Sex	Combined	8	8	8.91 (7.05-11.26)
		Males	5	5	9.56 (4.22-21.64)
		Females	10	10	9.33 (4.91-17.71)	NS
5	Region	N. America	13	10	8.91 (5.73-13.84)
		Europe	8	7	10.63 (6.93-16.29)
		Japan	2	1	6.00 (2.97-12.12)	NS
6	Study population	National	12	9	8.90 (6.47-12.24)
		Regional	11	9	9.51 (6.16-14.66)	NS
7	Year of start	< 1988	12	8	10.24 (7.26-14.45)
	of baseline	1988+	11	10	8.14 (5.78-11.47)	NS
8	Number of cases	< 1000	11	8	7.42 (5.65-9.74)
		1000+	12	10	10.67 (7.26-15.68)	NS
9	Exclusive cigarettes	No	13	12	9.02 (6.78-12.00)
		Yes	10	10	9.48 (5.25-17.14)	NS
10	Latency rule applied	No	21	16	8.41 (6.38-11.09)
		Yes	2	2	21.67 (7.74-60.66)	P < 0.1
11, 12	Lowest age considered	< 34	5	5	8.36 (7.13-9.80)
		35-45	5	4	6.26 (4.31-9.08)
		46-49	5	3	7.92 (5.41-11.58)
		50+	5	4	15.36 (5.95-39.66)	NS trend without
		Missing	3	2	9.33 (5.00-17.40)	Missing NS
13	Year of follow-up	< 10	6	4	6.85 (5.24-8.94)
		10- < 20	6	6	11.32 (6.67-19.20)
		20- < 30	9	7	10.11 (5.21-19.60)
		30+	2	1	6.29 (3.73-10.59)	NS trend NS
14	COPD definitiona	Excl. Bronch	6	5	17.45 (8.35-36.44)
		Incl. Bronch	5	3	7.83 (4.60-13.35)
		Other	12	10	7.15 (5.19-9.84)	P < 0.1
15	Endpoint	Died	13	8	10.95 (7.42-16.15)
		Diagnosed	10	10	7.49 (5.63-9.95)	NS
16	Number of adjustment factors	None	8	8	6.96 (5.09-9.53)
		More	15	10	10.83 (7.67-15.29)	P < 0.1

^aExcl. Bronch: Excluding bronchiectasis (codes 2 and 3 in Table 2); Incl. Bronch: Including bronchiectasis (codes 4, 6 and 7). COPD: Chronic obstructive pulmonary disease; RR: Relative risk; NS: Not significant.