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

Table 3 Lung cancer 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		62	44	12.14 (10.30-14.30)	P < 0.001
4	Sex	Combined	12	12	12.93 (10.55-15.84)
		Males	26	26	12.95 (9.82-17.08)
		Females	24	24	11.32 (8.46-15.15)	NS
5	Region	N. America	34	26	15.15 (12.77-17.96)
		Europe	21	14	12.30 (9.77-15.49)
		Japan	6	3	3.61 (2.87-4.55)
		Multi	1	1	13.10 (9.91-17.32)	P < 0.001
6	Study population	International	3	2	14.45 (6.85-30.50)
		National	25	16	10.26 (8.03-13.12)
		Regional	24	17	16.27 (13.39-19.77)
		Specific	10	9	9.71 (5.41-17.42)	P < 0.05
7	Year of start of baseline	< 1980	14	10	8.65 (5.83-12.83)
		1980-89	19	13	12.92 (9.83-16.98)
		1990-99	16	12	13.45 (9.76-18.53)
		2000+	13	9	14.38 (11.40-18.15)	NS trend P < 0.1
8	Number of cases	< 500	19	16	11.90 (9.55-14.83)
		500-1999	24	17	11.68 (8.65-15.75)
		2000+	19	11	12.76 (9.99-16.31)	NS trend NS
9	Exclusive cigarettes	No	45	35	13.47 (11.55-15.72)
		Yes	17	11	9.50 (6.61-13.64)	P < 0.1
10	Latency rule applied	No	51	38	11.93 (9.97-14.28)
		Yes	11	7	13.13 (8.69-19.83)	NS
11	Study design	Cohort	55	39	12.35 (10.35-14.73)
		Nested case control	7	5	10.41 (8.04-13.48)	NS
12, 13	Lowest age considered	< 30	15	10	11.30 (7.37-17.33)
		30-39	11	8	11.41 (7.80-16.70)
		40-48	14	9	13.29 (9.15-19.30)
		49+	14	10	13.62 (10.22-18.16)	NS trend without
		Missing	8	8	10.79 (7.64-15.23)	Missing NS
14	Year of follow-up	< 10	11	7	12.63 (8.49-18.80)
		10- < 15	11	8	16.05 (12.48-20.65)
		15- < 20	14	11	16.05 (12.69-20.30)
		20- < 30	15	11	9.08 (6.26-13.15)
		30+	11	8	9.57 (6.01-15.26)	P < 0.05 trend P < 0.1
15	Endpoint	Died	23	17	14.85 (11.99-18.38)
		Diagnosed	39	27	10.82 (8.61-13.60)	P < 0.05
16	Number of adjustment factors	None	20	15	9.65 (7.13-13.05)
		Age only	4	3	11.80 (5.24-26.56)
		More	38	28	13.68 (11.46-16.34)	NS trend P < 0.1

RR: Relative risk; NS: Not significant.