Table 1. The Newcastle-Ottawa scale (NOS) for assessing the quality of nonrandomized studies.

Not RCT (author, year)	Selection					Comparability			Exposure			Total points
	Is the case definition adequate?	Representativeness of the cases	Selection of controls	Definition of controls		Comparability of cases and controls on the basis of the design or analysis (age)	Comparability of cases and controls on the basis of the design or analysis (others)		Ascertainment of exposure	Same method of ascertainment for cases and controls	Non-response rate
Byun, 2013	*			*		*			*	*		5
Chen, 2012	*	*		*		*	*		*	*		7
Chen, 2011	*	*		*		*	*		*	*		7
Huang, 2014	*			*		*	*		*	*		6
Igai, 2014	*			*		*	*		*	*		6
Jutley, 2005	*			*		*	*		*	*		6
Kang, 2012	*			*		*	*		*			5
Kang, 2013	*			*		*	*		*	*		6
Kang, 2014	*			*		*	*		*	*		6
Li, 2014	*			*		*	*		*	*		6
Liang, 2013	*			*		*	*		*	*		6
Mao, 2014	*			*		*	*		*	*		6
Ocakcioglu, 2015	*			*		*	*		*	*		6
Salati, 2008	*	*		*		*			*	*		6
Song, 2015	*			*		*	*		*	*		6
Tsuboshima, 2015	*	*		*		*	*		*	*		7
Yang, 2013	*	*		*		*	*		*	*		7

RCT, randomized controlled trial.