Table 2.

Quality assessment under Newcastle-Ottawa scale.

Study	Case definition	Representativeness of the cases	Selection of controls	Definition of controls	comparability	Ascertainment of exposure	Same method for ascertainment for both cases and controls	Non-response rate	Score
Benito-Martin, 2013 (44)		*	*	*		*	*		5
Shankhajit De, 2017 (45)		*	*	*		*	*	*	6
Gudehithlu, 2015 (47)	*	*		*	**	*	*	*	8
Kalani, 2013 (36)		*	*	*	**	*	*	*	8
Sakurai, 2019 (46)	*	*	*	*		*	*		6
Sun, 2012 (40)		*	*	*	**	*	*		7
Zubiri, 2015 (38)	*	*	*	*	*	*	*		7
Zuviri, 2014 (39)		*	*	*	*	*	*		6
Kaminska, 2016 (13)		*	*	*	**	*	*		7
Luca Musante, 2015 (37)	*	*			*	*	*		5
Wu, 2018 (41)	*	*	*	*	*	*	*		7
Wang, 2020 (42)	*	*	*	*	*	*	*		7
Chen, 2021 (43)	*	*			*	*	*		5

*: The evaluation indicator had been conducted by the study.

**: In comparability section, if the most impartant factors were controlled then get *, if other second important factors were also controlled then get**