Table 5.

Newcastle-Ottawa scale for assessing quality of non-randomized studies

	Selection	Comparability	Outcome	Score
Parvini et al. [26]	★☆★★	☆☆	★★★	6/9
Schwarz et al. [27]	★☆★★	☆☆	★★★	6/9
Angermair et al. [28]	★☆★★	☆☆	★★★	6/9
Di Stefano et al. [29]	★☆★★	☆☆	★★★	6/9
Ortiz-Vigón et al. [30]	★☆★★	☆☆	★★★	6/9

0 to 3 stars = low-quality; 4 to 6 stars = moderate quality; 7 to 9 stars = high quality.