Table 3.

Quality assessment according to the Newcastle–Ottawa scale

Study	Selection	Comparability	Exposure	Total score
Holt (2008) [21]	3	1	3	7
Yip (2011) [22]	2	2	3	7
Desai (1998) [24]	2	2	3	7
McIntire (2018) [25]	3	1	2	6
McGinn (2019) [26]	3	2	3	8
Miller (2009) [27]	2	1	3	6
Kashefi (2014) [28]	3	2	3	8
Rivero (2007) [29]	3	1	3	7