Table 4.

Newcastle-Ottawa Quality assessment

Studies	Selection bias assessment				Comparability assessment	Outcome assessment			Total score
Tiihonen et al. 2012 [12]	*	*	*	*	*	*	–	*	8
Izumi et al. 2001 [13]	*	*	*	–	*	–	*	*	6
Isaranuwatchai et al. 2018 [14]	–	–	*	*	*	*	*	**	7
Alefan et al. 2019 [15]	*	*	*	*	*	–	–	*	6
Cowan et al. 2011 [17]	*	*	*	*	*	*	*	**	9
Swedler et al. 2019 [18]	*	*	*	*	**	*	*	*	9
Sari et al. 2016 [19]	*	*	*	*	*	**	*	*	9
Suárez-Bonel et al. 2015 [20]	*	*	*	*	*	*	*	*	8
Wacker et al. 2013 [21]	*	*	*	*	*	*	–	–	6