Study Country Ethnicity Experimental Control Mean SD Number Mean SD Nmuber Gabriel Moddel 2005 USA Caucasian 5.3 0.3 20 3 0.37 8 Iniad M Najm 2000 USA Caucasian 7.9 0.59 5 5.7 1.9 5 Jie Zheng 2011 China Asian 5 4.44 20 3 2.22 10

Table 2: Outcomes of included studies under experimental methods (NR2B, ICC).