Table 3.

Qualities of included studies evaluated by NOS (score)

Study	*Selection	Comparability	†Outcomes	Total scores
Chen et al.[19]	4	2	2	8
Cui et al.[25]	4	1	2	7
Ito et al.[20]	4	1	1	6
Jung et al.[21]	4	1	2	8
Kim EY et al.[22]	4	1	2	7
Kim HS et al.[23]	4	1	2	7
Lu et al.[24]	4	2	2	8

^*:1. Representativeness of exposed cohort; 2. Selection of non-exposed cohort; 3. Ascertainment of exposure; 4. Outcome not present at the start of the study; ^†:1. Assessment of outcomes, 2. Length of follow-up, 3. Adequacy of follow-up. NOS: the Newcastle-Ottawa Scale