Table 2. Quality assessment of included studies based on the Quality In Prognosis Studies (QUIPS).

Study	Quality evaluation of prognosis study						Total scorea	Level of evidenceb
	Study participation	Study attrition	Prognostic factor measurement	Outcome measurement	Study confounding	Statistical analysis and reporting
Hao 2016 [14]	Yes	Yes	Yes	Partly	Partly	Yes	6	2b
Ali 2016 [15]	Yes	Yes	Partly	Partly	Partly	Yes	6	2b
Wang 2015 [4]	Yes	Yes	Yes	Yes	Partly	Yes	7	1b
Lim 2015 [16]	Yes	Yes	Yes	Partly	Partly	Yes	8	1b
Kalniete 2015 [17]	Yes	Yes	Yes	Partly	Partly	Yes	7	1b
Chen 2014 [18]	Yes	Yes	Yes	Yes	Partly	Yes	7	1b
Wang 2014 [19]	Yes	Yes	Yes	Yes	Partly	Yes	7	1b
Wang (a)2013 [20]	Yes	Yes	Yes	Yes	Partly	Yes	8	1b
Wang (b) 2013 [21]	Yes	Yes	Yes	Partly	Partly	Yes	7	2b
Zhou 2013 [22]	Yes	Yes	Partly	Partly	Partly	Yes	5	2b
Xia 2012 [23]	Yes	Yes	Partly	Partly	Partly	Yes	6	2b
Marchini 2011 [24]	Yes	Yes	Yes	Yes	Partly	Yes	8	1b
Ueda 2010 [25]	Yes	Yes	Yes	Yes	Partly	Yes	8	1b

^a Quality assessment of included studies based on the Newcastle–Ottawa Scale.

^b The levels of evidence were estimated for all included studies with the Oxford Centre for Evidence Based Medicine criteria.