. 2021 Feb 27;24(3):159–168. doi: 10.1016/j.cjtee.2021.02.007

Table 2.

The quality of the retrospective control studies assessed with Newcastle–Ottawa scale.

Study (year)	Selection	Comparability	Exposure or outcome	NOS score
Chen et al.¹¹ (2019)	★★★	★	★★	6
Liu et al.¹² (2017)	★★★	★	★★★	7
Zhang et al.¹³ (2016)	★★★	★	★★	6
Wang et al.¹⁴ (2016)	★★★	★★	★★	7

Note: Newcastle–Ottawa scale (NOS). It contains 8 items, which are categorized into 3 dimensions: selection, comparability, and exposure (case-control study) or outcome (cohort study); a maximum of 4 stars could be given in “selection,” a maximum of 2 stars could be given in “comparability”, a maximum of 4 stars could be given in “exposure or outcome”. One star equated to 1 point, the full score was 10 points, and it was classified as low-quality literature when NOS score ≤5 points. The higher the score, the better the quality of the literature.