Table 1.

Quality assessment using Newcastle–Ottawa Scale (NOS).

Study, years	Selection				Comparability		Outcome			Total score	Quality
	Representativeness of Exposed cohort	Selection of Non-exposed cohort	Ascertainment of exposure	Outcome not present at start of study	a	b	Assessment of outcome	Follow-up long enough	Adequacy of follow-up
Cheng et al.16	★		★	★	★	★	★	★		7	Good
Bai et al.17	★		★		★	★	★	★		6	Fair
Liao et al.23	★		★		★	★	★	★		6	Fair
Zhu  et al.19	★		★	★	★	★		★		6	Fair
Shen et al.18	★	★	★		★	★		★	★	7	Good
Chen et al.24	★		★		★	★		★		5	Fair
Takahashi et al.20	★		★	★	★	★	★	★	★	8	Good
Raggi et al.25	★	★	★		★	★	★	★	★	8	Good
Panuccio et al.21	★		★		★	★	★	★		6	Fair
Wang et al.22	★		★		★	★	★		★	6	Fair

(a) The study controls for age (one star).

(b) Study controls for other factors (one star).