Table 7.

Checklist for observational cohort studies ⁽¹⁾, according to the Scottish Intercollegiate Guidelines Network.

Study	Q1	Q2	Q3	Q4	Q5	Score	Grade of evidence (2)
Zhang L., et al. [7]	Yes	Yes	No	No	No	2	–
Liu D., et al. [10]	Yes	Yes	No	No	No	2	–
Zeng L., et al. [17]	Yes	Yes	No	No	No	2	–

¹ One score for each checkpoint:

Q1 Are both groups selected from the same and well-defined cohort?

Q2 Is the proportion of dropout in each group known, and if so, is it <15 % in each?

Q3 Any comparison between full participants and those lost to follow-up?

Q4 Main potential confounders identified and considered?

Q5 Any confidence interval?

2.Grading was refined with a ‘+’ sign to suggest a low risk of bias for a score of 4 or 5, a ‘–’sign to suggest a high risk of bias for a score of 1 or 2, and no sign to suggest a moderate risk of bias for a score of 3.

Scottish Intercollegiate Guidelines Network. SIGN 50: a guideline developer’s handbook. Edinburgh, UK: SIGN, 2014.