Table 1.

Quality of the studies according to the Newcastle-Ottawa quality assessment scale.

Study	Selection	Comparability	Exposure	Total stars
Takane et al. 2002 [12]	∗∗∗∗	∗	∗∗∗	8
Sawamoto et al. 2005 [15]	∗∗∗∗	∗	∗∗∗	8
Takane et al. 2005 [13]	∗∗∗∗	∗	∗∗∗	8
Totan et al. 2006 [18]	∗∗∗∗	∗	∗∗∗	8
Greabu et al. 2006 [9]	∗∗∗	∗	∗∗	6
Badea et al. 2010 [19]	∗∗∗∗	∗	∗∗	5
Sezer et al. 2012 [14]	∗∗∗∗	∗∗	∗∗∗	9
Komatsu et al. 2013 [16]	∗∗∗	∗	∗∗∗	7
Dede et al. 2013 [7]	∗∗∗∗	∗	∗∗∗	8
Pendyala et al. 2013 [20]	∗∗∗∗	∗	∗∗∗	8
Miricescu et al. 2014 [8]	∗∗∗∗	∗	∗∗∗	8
Hernández-Monjaraz et al. 2014 [21]	∗∗	∗	∗∗	5
Baňasová et al. 2014 [22]	∗∗∗∗	∗	∗∗∗	8
Baltacioglu et al. 2014 [23]	∗∗∗∗	∗	∗∗∗	8
Trivedi et al. 2014 [24]	∗∗∗∗	∗	∗∗∗	8
Almerich-Silla et al. 2015 [6]	∗∗∗∗	∗∗	∗∗∗	9
Zamora-Perez et al. 2015 [17]	∗∗∗∗	∗∗	∗∗∗	9