Table 2.

Quality assessment scoring of included studies, according to NOS criterion

Author, year	Selection			Comparability1		Outcome assessment		Star Score
	1	2	3	4	5	6	7
Dulucq et al[28], 2005	*	*	*	*		*	*	******
Usui et al[9], 2005	*	*	*			*	*	*****
Kim et al[34], 2008	*	*	*			*		****
Mochiki et al[15], 2008	*	*	*	*		*	*	******
Topal et al[14], 2008	*	*	*	**	**	*		********
Kawamura et al[30], 2009	*	*	*	**	*	*	*	********
Sakuramoto et al[16], 2009	*	*	*	**		*	*	*******
Du et al[27], 2010	*	*	*	**		*	*	*******
Kim et al[33], 2011	*	*	*	**	*	*		*******
Eom et al[10], 2012	*	*	*			*	*	*****
Guan et al[17], 2012	*	*	*		*	*		*****
Siani et al[38], 2012	*	*	*	*	*	*	*	*******
Kim et al[32], 2013	*	*	*	**		*		******
Jeong et al[29], 2013	*	*	*	**	*	*		*******
Lee et al[37], 2013	*	*	*	**	*	*	*	********

Based on Newcastle-Ottowa Scale with maximum of *** for selection, ****for comparability, and ** for outcome assessment.

¹Comparability variables are (1) age, (2) sex, (3) body mass index, (4) American Society of Anesthesiologists, (5) comorbidity, (6) tumor size and (7) tumor stage. Group comparable for (1)-(3) or (4)-(7) (if yes, two stars, one star if one of these three characteristics was not reported, even if there were no other differences between the two groups and other characteristics had been controlled; no points were assigned if the two groups differed).