Table 4.

Bias assessment

Author	Selection				Comparability		Exposure/outcome			Biasa
	1	2	3	4	1a	1b	1	2	3
Anderson et al. [34]			*				*	*	*	4
Baker et al. [35]				*		*	*	*	*	5
Bilgin et al. [36]	*	*		*	*		*	*	*	7
Calu et al. [37]	*		*		*		*	*	*	6
Fouda et al. [38]	*	*		*	*		*	*	*	7
Jin et al. [39]	*			*			*	*	*	5
Komen et al. [40]	*	*		*			*	*	*	6
Li et al. [41]	*			*			*	*	*	5
Lohsiriwat et al. [42]	*		*				*	*	*	5
Mima et al. [43]	*	*		*			*	*	*	6
Palmisano et al. [44]				*			*	*		3
Reuvers et al. [45]	*	*		*			*	*	*	6
Sparreboom et al. [46]	*	*		*	*		*	*	*	7
Tominaga et al. [47]		*		*			*	*	*	5
van Praagh et al. [48]	*	*		*	*		*	*	*	7

^aAccording to the Newcastle–Ottawa scale