Table 2.

Study quality assessment using the Newcastle-Ottawa scale

Studies	Selection	Comparability	Outcome	Total stars
Cohort studies
Sørensen et al, 201529	⋆⋆⋆⋆	⋆⋆	⋆⋆⋆	9
Saltürk et al, 201519	⋆⋆⋆⋆	⋆	⋆⋆⋆	8
Duman et al, 201520	⋆⋆⋆⋆	⋆⋆	⋆⋆⋆	9
Lee et al, 201633	⋆⋆⋆⋆	⋆⋆	⋆⋆	8
Kumar et al, 201721	⋆⋆⋆⋆	⋆	⋆⋆⋆	8
Studies	Selection	Comparability	Exposure	Total stars
Cross-sectional studies
Tanrıverdi et al, 201536	⋆⋆⋆	⋆	⋆⋆⋆	7
Kurtipek et al, 20159	⋆⋆⋆⋆	⋆⋆	⋆⋆⋆	9
Bilir et al, 201623	⋆⋆⋆⋆⋆	⋆⋆	⋆⋆⋆	10
Furutate et al, 201630	⋆⋆⋆⋆	⋆⋆	⋆⋆⋆	9
Duyar, 201631	⋆⋆	–	⋆⋆⋆	5
Acartürk et al, 201735	⋆⋆⋆⋆	⋆	⋆⋆⋆	8
Studies	Selection	Comparability	Exposure	Total stars
Case-control studies
Günay et al, 201422	⋆⋆⋆⋆	⋆	⋆⋆⋆	8
Taylan et al, 201510	⋆⋆⋆⋆	⋆⋆	⋆⋆	8
In et al, 201624	⋆⋆⋆⋆	⋆	⋆⋆⋆	8
van de Geijn et al, 201632	⋆⋆⋆	⋆	⋆⋆⋆	7
Lee et al, 201625	⋆⋆⋆⋆	⋆⋆	⋆⋆⋆	9
Yousef and Alkhiary, 201726	⋆⋆⋆⋆	⋆⋆	⋆⋆⋆	9
Xiong et al, 201727	⋆⋆⋆⋆	⋆⋆	⋆⋆⋆	9
Rahimirad et al, 201737	⋆⋆⋆	⋆⋆	⋆⋆⋆	8
Mohamed-Hussein et al, 201734	⋆⋆⋆	–	⋆⋆⋆	6
Yao et al, 201738	⋆⋆⋆	⋆	⋆⋆⋆	7
Farah et al, 201728	⋆⋆⋆	⋆	⋆⋆⋆	7