Table 2.

Newcastle-Ottawa quality assessment scale.

First Author	Year	Selection	Comparability	Outcome	Total
Bai [20]	2015	★★★	★	★★★	7
Cai [11]	2010	★	★★	★★★	6
Deng [12]	2015	★★	★★	★★	6
Feng [14]	2017	★	★★	★★★	6
Li [10]	2015	★★	★	★★	5
Liu [16]	2013	★★	★★	★★★	7
Ma [23]	2008	★★	★★	★	5
Qian 1 [21]	2013	★★	★★	★★★	7
Qian 2 [21]	2013	★★	★★	★★★	7
Qian [13]	2016	★★	★★	★★★	7
Rong Shi [17]	2014	★★	★★	★	5
Meilin Shi [15]	2015	★★	★★	★★★	7
Tian [22]	2014	★★	★★	★★	6
Tian 1 [18]	2017	★	★★	★★★	6
Tian 2 [18]	2017	★	★★	★★★	6
Wang [19]	2017	★★	★★	★★★	7