Table 3.

Risk of bias assessment of the retrospective comparative studies and prospective controlled studies.

Study	Selection				Comparability	Outcome
	Exposed cohort	Non-exposed cohort	Ascertainment of exposure	Outcome of interest		Assessment of outcome	Length of follow-up	Adequacy of follow-up	Total score
Fan et al.	*	*	*	*	*	*	*	*	8
Francesco et al.	*	*	*	*	**	*	*	*	9
Francesco et al.	*	*	*	*	**	*	*	*	9
Hu et al.	*	*	*	*	*	*	*	*	8
Liu et al.	*	*	*	*	*	*	*	*	8
Wang et al.	*	*	*	*	*	*	*	*	8
Wang et al.	*	*	*	*	*	*	*	*	8
Wu et al.	*	*	*	*	*	*	*	*	8
Wu et al.	*	*	*	*	*	*	*	*	8

Risk of bias was assessed with use of the Newcastle–Ottawa Scale. “*” means a score of 1; “**” means a score of 2; the total score of this scale is 9. A higher overall score corresponds to a lower risk of bias; a total score of 5 or less indicates a high risk of bias.