Table 4.

Subgroup analysis of risk ratio based on participants expose to father smoking or mother smoking

Subgroup	Pooled risk ratio	95% confidence interval
Study participants
Father smoker
Anuntaseree (2001), Thailand	1.10	0.78 - 1.57
Ersu (2004), Turkey	3.53	1.34 - 9.30
Gill (2012), New Zealand	1.70	1.00 - 2.80
Sahin (2009), Turkey	1.62	0.89 - 2.93
Sogut (2009), Turkey	1.56	0.85 - 2.87
Subtotal	1.43	1.13 - 1.81
Mother smoker
Brunetti (2011), Italy	9.75	3.22 - 29.56
Ersu (2004), Turkey	3.48	1.61 - 7.51
Gill (2012), New Zealand	1.70	1.00 - 3.00
Li S (2010), China	1.65	1.34 - 2.02
Sahin (2009), Turkey	1.63	0.82 - 3.24
Sogut (2005), Turkey	2.19	0.70 - 6.84
Sogut (2009), Turkey	2.17	1.18 - 4.00
Subtotal	1.84	1.55 - 2.18