**0**wrote:

I want to combine three microarray datasets (E-TABM-158, GSE2034, and GSE3494) all of them from the same platform(HG-U133A). However, the raw data were normalized by RMA, MAS5, and global mean method. I want to find Fold change value for the combination set. Is it enough to use z-score before combine them and then calculate the FC value by this formula:

```
if((group2_mean(k)/group1_mean(k))>=1)
fc=(group2_mean(k)/group1_mean(k));
else
fc=-(group1_mean(k)/group2_mean(k));
end
```

Thank you in advance