Table 4.

Methodological quality of included studies determined by Newcastle-Ottawa scale.

Study	Selection	Comparability	Outcomes	Total
Noda et al., 199814	4	1	-	5
Wiklund et al., 200017	5	1	-	6
Aydin et al., 200418	4	2	-	6
Wakai et al., 200416	3	1	-	4
Chrysostomakis et al., 200619	3	2	-	5
Coruzzi et al., 200620	4	1	-	5
Aytemir et al., 200721	4	2	2	8
Zhu et al., 201222	4	1	2	7
Chang et al., 201324	5	2	-	7
Kim et al., 201523	5	2	-	7
Palma et al., 201525	4	2	-	6
Xie et al., 201715	3	1	-	4

Assessment strategy: selection (max. 5 stars), comparability (max. 2 stars) and outcome (max. 3 stars). Range 0-10 stars.