Table 4.

Quality assessment of nonrandomized studies using the modified Newcastle-Ottawa scale (NOS).

Study	Selection	Comparability	Outcome	Total	Quality
Abu-Rustum et al., 1997 [39]	***	*	***	*******	High
Pothuri et al., 2005 [40]	***	*	***	*******	High
Brard et al., 2006 [41]	***	**	***	********	High
Santarpia et al., 2006 [44]	***	n/a	***	******	Moderate
Chen et al., 2013 [42]	***	n/a	***	******	Moderate
Diver et al., 2013 [15]	***	**	***	********	High
Guerra et al., 2015 [47]	***	n/a	***	******	Moderate
Ansari et al., 2016 [46]	**	n/a	***	*****	Moderate
Chouhan et al., 2016 [43]	***	n/a	***	******	Moderate

Stars (*) are allocated as per NOS guidelines [34]. A maximum of 4 stars (Selection), 2 stars (Comparability) and 3 stars (Outcome) are allocated per category. n/a, not applicable.