Table 2.

Quality assessment of the studies included based on the Newcastle-Ottawa scale.

First Author	Selection				Comparability	Exposure			Total
	Adequate Case Definition	Representativeness of the Cases	Selection of Controls	Definition of Controls	Comparability of Cases and Controls	Ascertainment of Exposure	Method of Ascertainment	Non-Response Rate
Yasui-Furukori [13]	*	*	*	*	*	**	*		8
Ji L [14]	*	*	*	*	**	*	*		8
Azniza MR [15]	*		*	*	*	*	*		6
Li CI [16]	*	*	*	*	*	*	*		7
Akpalu J [17]	*	*	*	*	*	*	*		7
Fung ACH [18]	*	*	*	*	*	*	*		7
Ma Y [19]	*		*	*	*	*	*		6
Sidhu R [20]	*		*	*	*	*	*		6
Ismail K [21]	*	*	*	*	*	**	*		8
Arshad AR [22]	*	*	*	*	*	*	*		7
Brieler JA [23]	*		*	*	*	*	*		6
Mushtaque A [24]	*		*	*	*	*	*		6
Nicolau J [25]	*	*	*	*	*	**	*	*	9
Gorska-Ciebiada [26]	*	*	*	*	*	**	*		8
Ascher-Svanum H [27]	*	*	*	*	**	*	*		8
Zhang Y [11]	*	*	*	*	*	**	*		8
Zhang Y [11]	*	*	*	*	**	*	*		8
Luca A [29]	*	*	*	*	*	*	*		7
Palta P [30]	*		*	*	*	*	*		6
Zhang Y [28]	*	*	*	*	**	*	*		8
Hayashino Y [31]	*	*	*	*	**	*	*		8
Gorska-Ciebiada [32]	*	*	*	*	*	**	*		8
Tsujii S [33]	*		*	*	*	*	*		6
Mathew CS [34]	*		*	*	*	*	*		6
Hamer M [35]	*	*	*	*	*	*	*		7
Stanković Z [36]	*	*	*	*	*	*	*		7
Fisher L [37]	*		*	*	*	*	*		6
Calhoun D [38]	*	*	*	*	*	**	*	*	9
Yu R [39]	*		*	*	*	*	*		6
Egede LE [4]	*		*	*	*	*	*		6
Lee HJ [40]	*		*	*	*	*	*		6
Richardson LK [41]	*		*	*	*	*	*		6
Daly EJ [42]	*		*	*	*	*	*		6
de Groot M [43]	*		*	*	*	*	*		6

* One point, ** Two points.