Table 2

Quality assessment result using Newcastle-Ottawa Scale

Study	S					C		E/O				Total
Study	1	2	3	4	SUM	1	SUM	1	2	3	SUM	Total
Cantor et al (2018)	*	*	–	*	3	–	0	*	*	–	2	5
Deb et al (2014)	–	–	–	*	1	*	1	*	*	*	3	5
Hulsman (2007)	*	*	*	*	4	*	1	*	*	*	3	8
Ishikawa et al (2011)	*	*	*	*	4	**	2	*	*	*	3	9
Kawasaki et al (2013)	*	*	*	*	4	**	2	–	*	–	1	7
Kim H-A (2016)	*	*	*	*	4	**	2	*	*	*	3	9
Kim (2012)	*	*	*	*	4	*	1	–	*	*	2	8
Kim KE (2016)	*	*	*	*	4	**	2	–	*	*	2	8
Kyari et al(2016)	*	*	*	*	4	*	1	*	*	*	3	8
Memarzadeh et al (2010)	*	*	*	*	4	*	1	*	*	–	2	7
Onakoya et al (2009)	*	–	–	*	2	*	1	–	*	*	2	5
Shakya-Vaidya et al (2013)	*	–	–	*	2	*	1	*	*	*	3	6
Suzuki et al (2006)	*	*	*	*	4	**	2	–	*	–	1	7
Tham et al (2018)	*	*	*	*	4	**	2	–	*	–	1	7
Topouzis et al (2013)	*	*	*	*	4	*	1	–	*	*	2	7
Wang et al (2009)	*	*	*	*	4	**	2	*	*	*	3	9

C, comparability; E, exposure; O, outcome; S, selection.