Table 2.

Quality assessment of included studies according to the Newcastle-Ottawa Scale

Item/Study	Adequate definition of cases	Representativeness of cases	Selection of control subjects	Definition of control subjects	Control for important factor	Exposure assessment	Same method of ascertainment for all subjects	Non-response rate	Total
Hu XJ, 2019 [18]	1	0	0	1	1	1	1	1	6
Jin SY, 2019 [19]	1	0	0	1	2	1	1	1	7
Coto E, 2019 [20]	1	0	1	1	1	1	1	1	7
Seidi A, 2018 [21]	1	0	0	1	1	1	1	1	6
Luo JY, 2017 [22]	1	0	0	1	2	1	1	1	7
Lai HM, 2015 [23]	1	0	1	1	2	1	1	1	8
Lai H, 2015 [24]	1	0	1	1	2	1	1	1	8
Arslan S, 2015 [25]	1	0	0	1	2	1	1	1	7
Yang YN, 2015 [26]	1	0	1	1	2	1	1	1	8
Mishra A, 2013 [27]	1	0	0	1	2	1	1	1	7
Stegger JG, 2013 [28]	1	1	1	1	2	1	1	1	9
Mishra A, 2013 [27]	1	1	0	1	2	1	1	1	8
Xie FY, 2008 [15]	1	0	0	1	1	1	1	1	6