| Study |
Country |
Ethnicity |
Experimental |
Control |
| Mean |
SD |
Number |
Mean |
SD |
Number |
| Nobuhiro Mikuni 1999 |
USA |
Caucasian |
169 |
0 |
3 |
75 |
21 |
3 |
| Ying Z 1999 |
USA |
Caucasian |
168 |
13 |
11 |
76 |
9 |
11 |
| Zhong Ying 2004 |
USA |
Caucasian |
195 |
23 |
4 |
125 |
9 |
4 |
| Gabriel Moddel 2005 |
USA |
Caucasian |
90 |
14 |
20 |
41 |
13 |
8 |
|
