Table 2.

Quality assessment of included studies.

Study	Selection bias		Performance bias	Detection bias	Attrition bias	Reporting bias	Other bias
	Random sequence generation	Allocation concealment	Blinding of participants and personnel	Blinding of outcome assessment	Incomplete outcome data	Selective reporting	Other bias
Boonpiyathad 2017	?	+	–	–	+	+	+
Clark 1993	?	?	+	+	+	+	?
HERA Group 1995	+	+	+	+	+	+	?
Kravvariti 2020	+	+	–	–	+	–	+
Lee 2018	?	+	+	+	+	+	+
Liu 2019	+	+	+	+	+	+	+
Paton 2012	+	+	+	+	+	–	+
Van Gool 2001	+	+	+	+	+	+	+
Yokogawa 2017	+	+	+	+	+	–	?

+, low risk of bias; “?” Unclear risk of bias; “-” high risk of bias.