Table 3.

Risk of bias assessment for all included studies as determined using the Cochrane Risk of Bias guidelines. The symbol + represents low risk of bias; ? unclear risk of bias; − high risk of bias.

	Random Sequence Generation (Selection Bias)	Allocation Concealment (Selection Bias)	Blinding of Participants and Personnel (Performance Bias)	Blinding out Outcome Assessment (Detection Bias)	Incomplete Outcome Data (Attrition Bias)	Selective Reporting (Reporting Bias)	Other Bias
Abe et al. [28]	?	?	?	?	+	?	+
Clarkson et al. [29]	+	+	?	?	+	?	+
Cook et al. [30]	+	?	?	?	+	?	+
Harper et al. [31]	+	+	+	+	+	+	+
Kargaran et al. [32]	?	?	+	+	?	?	+
Letieri et al. [14]	+	+	+	+	+	+	+
Ozaki et al. [17]	+	+	?	?	?	?	+
Pereria et al. [33]	+	+	?	?	+	+	+
Yokokawa et al. [34]	+	+	?	?	+	+	+