Table 2. The methodological quality of included studies.

Study	A	B	C	D	E	F	Total
Jose 2001 [15]	+	+	+	+	+	?	5
Valerie 2005 [16]	+	+	+	+	+	?	5
Günther 2006 [17]	+	+	−	+	+	+	5
Schupbach 2007 [18]	+	+	−	+	+	?	4
Witt 2008[19]	+	+	+	+	+	+	6
Frances 2009 [20]	+	+	+	+	+	+	6
Laura 2009[21]	+	+	−	+	?	?	3
Adrian 2010 [22]	+	+	+	+	+	+	6
Kenneth 2010 [23]	+	+	+	+	+	+	6
Angelo 2011 [24]	+	−	+	+	?	?	3
Lee 2011 [25]	+	+	+	+	+	?	5
Laura 2012[26]	+	+	+	+	?	?	4
Frances 2012 [27]	+	−	+	+	+	?	4
Michael 2012 [28]	+	+	−	+	+	+	5
Schuepbach 2013 [29]	+	+	+	+	+	+	6
Vincent 2013 [10]	+	+	+	+	+	+	6

A: Sequence generation; B: Allocation concealment; C: Blinding of participants, personnel and outcome assessors;

D: Incomplete outcome data; E: No selective outcome reporting; F: Other sources of bias; +: Yes; −: No; ?: Unclear.