Table 2.

Cochrane Collaboration Risk of Bias assessment summary

	Study	Sequence generation	Allocation concealment	Blinding of participants and personnel	Blinding of outcome assessment	Incomplete outcome data	Selective reporting	Other bias	Overall risk of bias
1	Fassoulaki et al. (2002)	+	+	+	+	+	?	+	+
2	Fassoulaki et al. (2005)	+	+	+	+	+	?	+	+
3	Nikolajsen et al. (2006)	+	+	+	+	?	?	?	?
4	Kinney et al. (2012)	+	+	+	+	?	?	+	?
5	Amr and Yousef (2010)	+	+	+	+	?	?	+	?
6	Dualé et al. (2009)	+	+	+	+	?	+	+	+
7	Hayes et al. (2004)	+	+	+	+	+	?	+	+
8	Mendola et al. (2012)	+	+	+	+	+	?	+	+
9	Joseph et al. (2012)	+	+	+	+	?	+	+	+
10	Wilson et al. (2008)	+	+	+	+	?	+	+	+
11	Ryu et al. (2011)	+	+	+	+	?	+	+	+
12	Ju et al. (2008)	?	+	+	+	?	?	+	?
13	Yang et al. (2004)	+	+	+	+	?	?	+	?
14	Mustola et al. (2011)	?	+	+	+	?	?	+	?
15	Sepsas et al. (2013)	?	+	+	+	?	?	?	?
16	Gwak et al. (2004)	?	+	+	+	?	?	+	?
17	Lu et al. (2013)	+	+	+	+	+	?	+	+
18	Cerfolio et al. (2003)	?	+	+	+	+	?	+	+
19	Vigneau et al. (2011)	+	+	+	+	+	?	+	+
20	Albi-Feldzer et al. (2013)	+	+	+	+	+	?	+	+
21	Baudry et al. (2003)	+	+	+	+	?	?	+	?
22	Grigoras et al. (2012)	+	+	+	+	+	?	+	+
23	Fassoulaki et al. (2000)	?	+	+	+	+	?	+	+
24	Obata et al. (1999)	?	+	+	+	+	?	+	+
25	Senturk et al. (2002)	?	−	−	+	+	?	+	−
26	Ochroch et al. (2002)	?	+	+	+	+	?	+	?
27	Salengros et al. (2010)	?	+	+	+	+	?	+	+
28	Nikolajsen et al. (1997)	?	+	+	+	?	?	?	?
29	Kairaluoma et al. (2006)	+	+	+	+	+	?	+	+
30	Ibarra et al. (2011)	?	+	?	+	−	?	+	−
31	Karanikolas et al. (2011)	+	+	+	+	+	+	+	+
32	Song et al. (2012)	+	+	+	+	+	?	+	+

‘+’, low risk of bias (unlikely to seriously alter the results); ‘?’, unclear risk of bias (raises some doubt about the results); ‘−’, high risk of bias (seriously weakens confidence in the results). The far right column (in bold) gives overall risk of bias based on all the values within an entire row.