Table 1.

Quality of studies evaluated by the modified Newcastle-Ottawa scale

Ref.	Selection				Comparability		Outcome		Quality score
	Case definition	Representativeness	Selection of controls	Definition of controls	Comparable for therapy	Comparable for etiology	Assessment of outcomes	Integrity of follow-up
Xia et al[24]	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	★★★★★★★★
Lai et al[25]	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	★★★★★★★★
Parisi et al[26]	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	★★★★★★★★
Nicolini et al[27]	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	★★★★★★★★
Harimoto et al[28]	Yes	Yes	No	Yes	Yes	Yes	Yes	Yes	★★★★★★★★