Risk of bias of included studies
As shown in Table S3 andFigure S2 , there were no specific descriptions about random
sequence generation in nine studies (31, 48, 50, 60, 65, 72, 74, 77) and
they were determined to be “unclear”. There were 5 studies with both a
sham group and a no treatment control (35, 40, 64, 74, 77) which were
defined as unclear risk for blinding of participants. However, studies
with no treatment control were scored as high risk of bias. In all
included studies, there was no attrition bias from reviewing methods and
results. Since results could be directly obtained, reporting bias was
assessed as ‘low risk’ for all included studies. In addition, other
sources of bias such as improper funding were not described and were at
unclear risk of this bias.