Table 2. Study quality assessment according to the NOS.

Authors	NOS
	Selection	Comparability	Outcome	Total (maximum 8)	Quality judgementa
Badhwar et al. [2019] (20)	4	1	2	7	High
Bolling et al. [2010] (19)	4	1	1	6	Fair
Chikwe et al. [2017] (21)	4	1	3	8	High
Ch’ng et al. [2015] (11)	4	–	2	6	Fair
Hannan et al. [2019] (22)	4	1	2	7	High
Kilic et al. [2013] (23)	4	1	1	6	Fair
LaPar et al. [2014] (24)	4	1	2	7	High

^a, ≤5: low methodological quality, 6: fair methodological quality, ≥7: high methodological quality. NOS, Newcastle-Ottawa Scale.