Table 3.

Quality assessment of nonrandomized studies.

Studies	Selection	Comparability	Outcome	Score
Hou et al[15]	★★★	★	★★★	7
Hastaoğlu et al[14]	★★★★	★	★★★	8
Wang et al[17]	★★	★	★★★	6
Jiao et al[18]	★★	★	★★★	6

The Cohort studies were evaluated using the Newcastle–Ottawa scale, which are comprised of the study of selection (representativeness of the exposed group, representativeness of the non exposed group, ascertainment of exposure, demonstration that outcome of interest was not present at start of study), group comparability (controls for the most important factor, controls for any additional factor), and outcome measures (assessment of outcome, was follow-up long enough for outcomes to occur, adequacy of follow-up of cohorts); a total of 9 points. ★, 1 point.