Environmental tobacco smoke exposure and lung cancer: A systematic review

Table 3 Meta-analyses of smoking by the spouse (or nearest equivalent)

Estimates considered	No. of estimates	Relative risk (95% confidence limits)		Heterogeneity1
		Fixed-effects meta-analysis	Random-effects meta-analysis
All	119	1.18 (1.14-1.23)	1.21 (1.14-1.29)	+++
N America	38	1.08 (1.00-1.17)	1.09 (0.95-1.26)	+++
Europe	22	1.15 (1.03-1.28)	1.16 (1.00-1.35)	(+)
Asia	54	1.24 (1.17-1.32)	1.31 (1.20-1.44)	+++
Asia - Japan	13	1.26 (1.11-1.45)	1.26 (1.11-1.45)	NS
Asia - Hong Kong	8	1.32 (1.12-1.57)	1.31 (1.06-1.63)	NS
Asia - China	23	1.16 (1.06-1.27)	1.29 (1.08-1.54)	+++
Asia - Other	10	1.34 (1.19-1.51)	1.37 (1.19-1.57)	NS
Heterogeneity between Asian countries				NS
Other continents	5	1.20 (1.09-1.33)	1.20 (1.09-1.33)	NS
Heterogeneity between continents				(+)
Published in 1981-1989	34	1.38 (1.24-1.54)	1.38 (1.24-1.54)	NS
Published in 1990-1999	33	1.09 (1.01-1.17)	1.15 (1.02-1.28)	++
Published in 2000-2009	34	1.22 (1.12-1.33)	1.21 (1.08-1.36)	+
Published in 2010 onwards	18	1.17 (1.10-1.26)	1.13 (0.94-1.36)	+++
Heterogeneity by publication date				++
1-49 cases	23	1.44 (1.14-1.81)	1.47 (1.15-1.88)	NS
50-99	31	1.30 (1.14-1.47)	1.27 (1.08-1.50)	+
100-199	29	1.09 (1.00-1.19)	1.10 (0.96-1.26)	+++
200-399	22	1.33 (1.21-1.46)	1.32 (1.16-1.50)	+
400+	14	1.14 (1.07-1.20)	1.13 (1.02-1.25)	++
Heterogeneity by study size				++
Case-control	97	1.18 (1.13-1.23)	1.22 (1.13-1.31)	+++
Prospective	22	1.18 (1.05-1.33)	1.18 (1.05-1.33)	NS
Heterogeneity by study type				NS
Not age adjusted	21	1.34 (1.19-1.50)	1.42 (1.18-1.71)	+
Age adjusted	98	1.16 (1.11-1.21)	1.18 (1.10-1.26)	+++
Heterogeneity by age adjustment				NS
Dose-response results not reported	46	1.13 (1.06-1.21)	1.18 (1.06-1.31)	++
Only no dose-response stated	2	0.95 (0.60-1.50)	0.95 (0.60-1.50)	NS
Dose-response results reported	71	1.21 (1.15-1.28)	1.24 (1.14-1.35)	+++
Heterogeneity by dose response reporting				NS
Spouse the index	71	1.18 (1.11-1.24)	1.21 (1.12-1.31)	++
Spouse not the index	48	1.19 (1.12-1.27)	1.20 (1.07-1.35)	+++
Heterogeneity by index definition				NS

¹Significance levels indicated by +++ P < 0.001, ++ P < 0.01, + P < 0.05, (+) P < 0.1 for heterogeneity within level and for heterogeneity between level. NS: Not significant, P≥ 0.1.