Table 2.

Risk of bias according to Cochrane's risk of bias assessment tool for included non-randomized controlled trials.

References	Confounding bias	Selection bias	Deviation from intended intervention	Missing data	Measurement in outcome	Selection of reported result	Classification of intervention	Level of evidence
Hou et al. (46)	+	+	+	?	+	–	+	2b
Ye et al. (50)	+	+	+	?	+	–	+	2b
Liu et al. (47)	+	+	+	?	+	–	+	2b
Sato et al. (48)	+	–	+	?	+	–	+	2b
Wang et al. (49)	+	+	?	+	+	?	+	2b
Zhou et al. (28)	+	+	+	+	+	+	+	2b
Hutanu et al. (35)	+	–	+	+	?	–	+	2b
Nezu et al. (27)	+	?	+	–	+	?	+	2b
Fukuda et al. (25)	+	?	+	–	+	?	+	2b
Liu et al. (26)	+	–	+	?	+	–	+	2b
Hsu et al. (44)	+	?	+	?	+	+	+	2b
Chen et al. (29)	+	?	+	–	+	?	+	2b
Kim et al. (32)	+	?	+	+	+	+	+	2b
Hu et al. (33)	+	+	+	+	+	+	–	2b
Yang et al. (51)	+	+	+	+	+	+	+	2b
Chiu et al. (30)	+	?	+	+	+	+	+	2b
Krarup et al. (45)	+	?	+	–	+	?	+	2b
Üstündag et al. (34)	+	–	+	+	+	–	–	2b
Delgado et al. (31)	+	–	+	+	+	–	+	2b