Table 2.

The risk of bias of the included studies

Author	Random sequence generation	Allocation concealment	Blinding of participants and personnel	Blinding of outcome assessment	Incomplete outcome data	Selective reporting	Other bias
Ahn et al. [18] 2013	Low risk	Unclear	Unclear	Unclear	High risk	Low risk	Low risk
Ritsuno et al. [21] 2014	Unclear	Low risk	Unclear	Unclear	Low risk	Low risk	Low risk
Koike et al. [19] 2015	Low risk	Low risk	Unclear	Unclear	Low risk	Low risk	High risk
Mori et al. [20] 2017	Unclear	Low risk	Unclear	Unclear	Low risk	Low risk	Unclear
Yamasaki et al. [22] 2018	Low risk	Unclear	High risk	Unclear	Low risk	Low risk	Unclear
Yoshida et al. [23] 2018	Low risk	High risk	High risk	Unclear	Low risk	Low risk	Unclear
Ban et al. [24] 2018	Low risk	Unclear	Unclear	Unclear	Low risk	Low risk	High risk