Table 4.

Quality assessment of the retrieved studies

Ref.	Q1	Q2	Q3	Q5	Q6	Q15	Q18	Q25
	Hypothesis clearly described	Main outcomes clearly described in the introduction or methods section	Participants characteristics clearly described	Distributions of confounders in each group of subjects clearly described	Main study findings clearly described	Study measurement blind	Appropriateness of the statistical tests	Adjustment for confounding
Kazlouski et al[13]	Yes	Yes	Yes	No	Yes	U	U	No
Frank et al[49]	Yes	Yes	Yes	Partially	Yes	U	Yes	Yes
Nagahara et al[7]	Yes	Yes	Yes	No	Yes	U	Yes	No
Via et al[53]	Yes	Yes	Yes	Yes	Yes	U	Yes	Yes
Frieling et al[5]	Yes	Yes	Yes	Yes	Yes	U	Yes	Yes
Yau et al[39]	Yes	Yes	Yes	No	Yes	U	Yes	No

Q4 regarding to interventions of interest clearly described was not applicable to this review since any of the studies undertook an interventional design. Yes scored as 1, No scored as 0, Partially scored as 0.5. U: Unable to determine.