Table 3.

Risk of bias assessment of the CSs

Study	Selection					Outcome
	Exposed cohort	Nonexposed cohort	Ascertainment of exposure	Outcome of interest	Comparability	Assessment of outcome	Length of follow-up	Adequacy of follow-up	Total score
Wu et al. [23]	*	*	*	*	**	*	*	*	9
Takasaka et al. [24]	*	*	*	*	–	*	*	*	7
Kline et al. [25]	*	*	*	*	**	*	–	–	7
Weber et al. [26]	*	*	*	*	**	*	*	*	9
Yeo et al. [27]	*	*	*	*	**	*	*	*	9

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