Table 2.

Newcastle-Ottawa scale for observational studies.

Author	Year	Selection	Comparability	Outcomes	Quality judgment
Alsalmi	2019	4	2	3	9
Jin	2021	4	1	2	7
Lin	2020	4	2	2	8
Wang	2021	4	1	2	7
Yuan (d)	2020	4	2	2	8
Yuan (s)	2020	4	2	2	8

Selection: (1) representativeness of the exposed cohort, (2) selection of the nonexposed cohort, (3) ascer tainment of exposure and (4) demonstration that outcome of interest was not present at the start of stud.

Comparability: comparability of cohorts on the basis of the design or analysis.

Outcomes: (1) assessment outcome, (2) was follow-up long enough for outcomes to occur, (3) adequacy of follow-up of cohorts (≥1 years).

NOS scores ≥ 7 indicate a high-quality study.