Table 2.

Risks of bias in the included studies

References	Randomization	Allocation concealment	Double blinding	Handling of dropouts	Similarity of groups at baseline
Niki et al. [26]	?	?	+	+	+
Shehata et al. [22]	+	+	−	+	+
Zúñiga et al. [23]	+	+	+	+	+
Wu et al. [24]	?	?	+	+	+
Shaikh et al. [14]	−	−	−	+	+
Kanai et al. [25]	?	?	?	+	+
Kanai et al. [27]	+	+	?	+	+
Zakrzewska et al. [15]	+	?	+	+	+
Kondziolka et al. [21]	+	+	+	+	+
Fromm et al. [17]	?	?	+	+	?
Lechin et al. [20]	+	?	+	+	+
Lindström and Lindblom [19]	?	?	?	+	−
Vilming et al. [16]	?	?	?	+	−
Fromm et al. [18]	?	?	+	+	+
Nicol [10]	+	?	+	+	?
Kilian and Fromm [11]	+	?	+	+	?
Rockliff and Davis [12]	+	+	+	+	?
Campbell et al. [13]	+	?	+	?	?

+ risk of bias item handled correctly and described, − risk of bias item not handled correctly, ? not clear