Environmental tobacco smoke exposure and lung cancer: A systematic review

Table 4 Meta-analyses of childhood environmental tobacco smoke exposure

Estimates considered	No. of estimates	Relative risk (95% confidence limits)		Heterogeneity1
		Fixed-effects meta-analysis	Random-effects meta-analysis
From any cohabitant	41	1.08 (1.01-1.15)	1.15 (1.02-1.29)	+++
N America	13	1.00 (0.89-1.13)	1.06 (0.89-1.28)	+
Europe	11	0.94 (0.81-1.08)	1.02 (0.81-1.29)	+
Asia	15	1.26 (1.11-1.42)	1.31 (1.02-1.67)	+++
Other	2	1.10 (0.95-1.28)	1.13 (0.89-1.45)	NS
Heterogeneity between continents				+
From mother specifically	9	0.96 (0.77-1.20)	0.98 (0.77-1.25)	NS
From father specifically	11	0.90 (0.80-1.00)	1.00 (0.78-1.29)	+++
From parents specifically	8	0.78 (0.64-0.94)	0.78 (0.64-0.94)	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.