Table 3.

Quality of cohort studies evaluated by modified Newcastle-Ottawa scale

Ref.	Selection				Comparability		Outcomes		Quality score
	Definition of cases	Representativeness	Selection of controls	Definition of controls	Comparable for 1, 2, 3, 4	Comparable for 5, 6, 7	Assessment of outcomes	Integrity of follow-up
Cai et al[16], 2007	Yes	No	No	Yes	Yes	5	Yes	Yes	7
Li, H et al[18], 2008	Yes	No	No	Yes	1, 2	5	Yes	Yes	5
Jin et al[19], 2015	Yes	No	No	Yes	1, 2, 3	No	Yes	Yes	5
Kim et al[20], 2015	Yes	Yes	No	Yes	1, 3, 4	6, 7	Yes	Yes	7
Lee et al[21], 2014	Yes	No	No	Yes	1, 2, 4	5	Yes	Yes	6
Li, J et al[22], 2014	Yes	No	No	Yes	1, 2, 3	6	Yes	Yes	6
Li, Y et al[23], 2015	Yes	No	No	Yes	1, 2, 3	No	Yes	Yes	5
Namgoong et al[24], 2014	Yes	No	No	Yes	Yes	6	Yes	Yes	7
Peng et al[25], 2016	Yes	Yes	No	Yes	Yes	No	Yes	Yes	7
Shin et al[26], 2015	Yes	No	No	Yes	1, 2	No	Yes	Yes	5
Song et al[27], 2010	Yes	No	No	Yes	Yes	6	Yes	Yes	7
Tian et al[28], 2013	Yes	No	No	Yes	1, 2, 4	5	Yes	Yes	6
Tu et al[29], 2010	Yes	Yes	No	Yes	Yes	No	Yes	Yes	7
Ye et al[30], 2015	Yes	Yes	No	Yes	Yes	No	Yes	Yes	7

1: Age; 2: Sex; 3: Liver function; 4: Previous upper surgery history; 5: Surgeon experience; 6: Body mass index; 7: American Society of Anesthesiologists score.