Table 3.

Quality assessment of the included case-control studies using the Newcastle-Ottawa Scale (NOS)

	Selection				Comparability/ confounders	Exposure			Total
Author	Adequacy of case definition (⋆)	Representativeness of the cases (⋆)	Selection of controls (⋆)	Definition of controls (⋆)	Comparability of cases and controls (⋆⋆)	Ascertainment of the exposure (⋆)	Similarity of ascertainment between cases and controls (⋆)	Non-response rate (⋆)	(*9)
Khalawi et al., 2017 [9]	–	*	–	–	–	–	*	–	2
Youssef et al., 2016 [42]	*	*	–	*	*	–	*	–	5
Alzahrani AJ, 2008 [38]	–	*	–	–	*	–	*	–	3
Chinnian et al., 1994 [43]	–	*	–	*	*	–	*	–	4