2.3. Quality Assessment

Quality assessment of the studies was performed by the Newcastle–Ottawa scale (NOS) checklist for cross-sectional studies [16]. This checklist consisted of the parts' selection (in turn, including representativeness of the sample 0-1 point, sample size 0-1 point, nonrespondents 0-1 point, and ascertainment of the exposure 0–2 points), comparability 0 and 2 points, and outcome (in turn, including assessment of outcome 0–2 points and statistical tests 0-1 point). The total scoring categories were unsatisfactory (<5 points), satisfactory (5-6 points), good (7-8 points), and very good (8–10 points). The process was conducted by two independent researchers.