Table 4. Risk of bias according to Cochrane risk of bias tool.

Study	Random sequence generation	Allocation concealment	Blinding of participants and personnel	Blinding of outcome assessor	Incomplete data	Selective reporting
Tyler, 2017	?	?	+	+	-	-
Mei, 2014	?	?	?	?	?	?

? Unclear risk of bias;—low risk of bias; + high risk of bias.