Table 1.

Risks of bias assessment

Study	Selection bias		Performance bias Blinding of participants and personnel	Detection bias Blinding of outcome assessment	Attrition bias Incomplete outcome data	Reporting bias Selective reporting
	Random sequence generation	Allocation concealment
van der Wijk et al. (1998)	Low	Low	Low	Low	Low	Low
Takanashi et al. (2004)	Low	Unclear	Low	Unclear	Low	Low
Stoker et al. (2007)	Low	Unclear	Low	Unclear	Low	Low
Walton et al. (2009)	Low	Unclear	High	High	Low	Low
Cristache et al. (2012)	High	High	High	Low	Low	Low
Heydecke et al. (2005)	Low	Unclear	Low	Unclear	Low	Low
Zitzmann et al. (2006)	High	High	High	High	Low	Low
Della Vechia et al. (2017)	Low	Low	Low	Unclear	Low	Low
Jawad et al. (2017)	Low	High	High	Low	Low	Low