Table 2.

Quality Assessment of Studies Using Newcastle–Ottawa Scale for Case–control Studies

Authors, year	Selection				Comparability of cases and controls (matched for)	Exposure			Total score
	Adequate definition of cases	Representativeness of cases	Selection of controls	Definition of controls		Ascertainment of exposure	Same method of ascertainment for cases and controls	Non-response rate
Baylan, F. A., [19]	*	*	–	*	**	*	*	–	7
Du, C., [20]	*	*	*	*	**	*	*	–	8
Cataldo, L. R., [22]	*	*	–	*	**	*	*	*	8
Jiang Fen, [23]	*	*	–	*	**	–	*	–	6
Wojciechowska M, [24]	*	*	*	*	**	*	*	–	8
Wang Xiaogang, [25]	*	*	–	*	**	*	*	–	7