Study leave out

Pooled RR

95% CI

P value

Heterogeneity (P value, I²)

Arnold 2009 [12]

0.76

[0.64, 0.90]

0.001

(0.26, 20%)

Buchfelder 2007 [14]

0.74

[0.63, 0.88]

0.0005

(0.45, 0%)

Brignardello 2015 [13]

0.76

[0.64, 0.89]

0.001

(0.28, 18%)

Child 2015 [20]

0.77

[0.64, 0.94]

0.008

(0.23, 24%)

Hartman 2013 [15]

0.8

[0.67, 0.95]

0.01

(0.31, 15%)

Hatrick 2002 [16]

0.77

[0.65, 0.91]

0.002

(0.23, 24%)

Mackenzie 2013 [17]

0.76

[0.64, 0.90]

0.001

(0.26, 21%)

Olsson 2009 [18]

0.76

[0.64, 0.91]

0.003

(0.22, 25%)

Olsson 2012 [19]

0.81

[0.69, 0.96]

0.02

(0.70, 0%)

Olsson 2017 [21]

0.75

[0.63, 0.90]

0.002

(0.24, 23%)

None

0.77

[0.65, 0.90]

0.001

(0.3, 15%)