Table S2. Methodological quality of nested case-control studies included in the meta-analysis*.

Reference (first author, year)	Adequate definition of cases	Representativeness of cases	Selection of control subjects	Definition of control subjects	Control for important factor or additional factor†	Exposure assessment	Same method of ascertainment for all subjects	Nonresponse rate‡	Total quality scores
Qu (a), 2014	☆	–	☆	☆	☆	☆	☆	☆	7
Qu (b), 2014	☆	–	☆	☆	☆	☆	☆	–	6
Munoz, 2011	☆	–	☆	☆	☆	☆	☆	☆	7
Yuan, 2009	☆	☆	☆	☆	☆☆	☆	☆	☆	9
Sung, 2009	☆	–	☆	☆	–	☆	☆	–	5
Fang (a), 2008	☆	–	☆	☆	☆☆	☆	☆	☆	8
Chou, 2008	☆	–	☆	☆	–	☆	☆	–	5
Cao, 2008	☆	☆	☆	☆	–	☆	☆	☆	7
Guo, 2008	☆	☆	☆	☆	–	☆	☆	☆	7
Zhu, 2008	☆	☆	☆	☆	–	☆	☆	☆	7
Zhang, 2007	–	☆	☆	☆	☆	☆	☆	☆	7
Kao, 2003	☆	☆	☆	☆	☆	☆	☆	☆	8

*, a study could be awarded a maximum of one star for each item except for the item Control for important factor or additional factor; ^†, a maximum of 2 stars could be awarded for this item. Studies that matched or controlled for age and sex received one star, whereas studies that controlled for more than 3 of other important confounders such as alcohol drinking, smoking, HBV DNA, Genotype, HBeAg, ALT, liver cirrhosis received an additional star; ^‡, a One star was assigned if there was no significant difference in the response rate between control subjects and cases by using the chi-square test (P<0.05).