Table 3. Quality assessment of eligible studies with Newcastle-Ottawa Scale.

First author	Year	NOS	Selection	Comparability	Outcome
Bian	2015	6	★★★*	★	★★*
Chang	2015	8	★★★	★★	★★★
Cinti	2008	7	★★★	★★	★★
Han	2011	7	★★★*	★*	★★★
Kobayashia	2006	6	★★★	★	★★*
Liang	2015	6	★★*	★★*	★★*
Luber	2011	7	★★★	★	★★★*
Murakami	2007	8	★★★	★★	★★★*
Murayama	2009	8	★★★	★★*	★★★
Nam	2003	6	★★★*	★★	★*
Sasaki	2014	7	★★	★★	★★★*
Sukawa	2012	7	★★★*	★	★★★*
Xue	2012	6	★★★	★*	★★

*The score was produced by discussion.