Table 2.

Quality assessment of individual study

Study	Allocation sequence generation	Allocation concealment	Blinding	Loss to follow-up	Calculation of sample size	Statistical analysis	Intention-to-treat analysis	Level of quality
Yamaguchi O [8]	A	A	A	70	Yes	The paired t test	Yes	A
Gotoh M [6]	A	A	A	11	Yes	The paired t test	Yes	A
Lee KS [11]	A	A	A	7	Yes	The paired t test	Yes	A
Homma Y [10]	A	A	A	47	Yes	The paired t test	Yes	A
Yamaguchi O [9]	A	A	A	64	Yes	The paired t test	Yes	A
Sener NC [15]	A	A	A	0	Yes	The paired t test	Yes	A
Bae JH [14]	A	B	B	43	Yes	The paired t test	Yes	B
Yokoyama T [13]	A	A	A	2	Yes	The paired t test	Yes	A
Lee KS 12	A	A	A	2	Yes	The paired t test	Yes	A

A all quality criteria met (adequate): low risk of bias. B one or more of the quality criteria only partly met (unclear): moderate risk of bias. C one or more criteria not met (inadequate or not used): high risk of bias