Table 2.

The quality of the case-control studies and cohort studies.

	Study	Year	Selection	Comparability	Outcome	Starsa
1	Yin et al.	2004	3	2	2	7
2	Wu et al.	2004	4	2	2	8
3	Ma et al.	2004	3	2	2	8
4	Loeb et al.	2004	3	2	2	7
5	Teleman et al.	2004	3	2	3	8
6	Wilder-Smith et al.	2005	3	2	3	8
7	Nishiura et al.	2005	4	2	1	7
8	Cheng et al.	2010	3	2	3	8
9	Jaeger et al.	2011	3	2	2	7
10	Chokephaibulkit et al.	2012	3	2	2	7
11	Zhang et al.	2012	3	2	3	8
12	Zhang et al.	2013	4	2	1	7
13	Sung et al.	2016	3	2	2	7
14	Zhang et al.	2017	3	2	1	6
15	Wang et al.	2020	3	1	1	5

^aScoring by Newcastle-Ottawa Scale.