Table 2.

Quality assessment for the selected retrospective cohort studies according to the Newcastle Ottawa Scale (NOS)

References	Selection	Comparability	Outcome/exposure	Overall score
Kubat et al. [22]	***	–	***	6/9
Anderson et al. [9]	****	*	***	8/9
Kudsi et al. [25]	***	–	***	6/9
Hosein et al. [21]	***	*	***	7/9
Robinson et al. [12]	****	*	***	8/9