Table 2. The quality assessment of included studies.

	Newcastle-Ottawa Scale*
Author	1	2	3	4	5A	5B	6	7	8	Total
Ho [22]	Yes	Yes	No	Yes	Yes	No	Yes	Yes	Yes	7
Montavon [16]	Yes	Yes	No	Yes	Yes	No	Yes	Yes	Yes	7
Bhagat [23]	Yes	Yes	No	Yes	Yes	No	Yes	Yes	Yes	7
He [24]	Yes	Yes	No	Yes	Yes	No	Yes	Yes	Yes	7
Chen [17]	Yes	Yes	No	Yes	Yes	No	Yes	Yes	Yes	7
Shen [25]	Yes	Yes	No	No	Yes	No	Yes	Yes	Yes	6
Wu [18]	Yes	Yes	No	Yes	No	No	Yes	Yes	Yes	5
Li [26]	Yes	Yes	Yes	Yes	Yes	No	Yes	Yes	Yes	8
Makarla [27]	Yes	Yes	No	Yes	Yes	No	Yes	Yes	Yes	7
Ma [19]	Yes	No	No	Yes	Yes	No	Yes	Yes	Yes	5
Ibanez [20]	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	Yes	8
Rathi [28]	Yes	Yes	No	Yes	Yes	No	Yes	Yes	Yes	7
Yoon [21]	Yes	Yes	No	Yes	Yes	No	Yes	Yes	Yes	7

^*1 indicates case definition and diagnostic appropriate; 2, consecutive patients or case having a good representation; 3, community controls; 4, control with no the history of study disease; 5A, according to the most important factor to select and analyze control; 5B, according to the second important factor to select and analyze control; 6, ascertainment of exposure by blinded interview or record; 7, same method of ascertainment used for cases and controls; and 8, non-response rate the same for cases and controls.