[BioC] fold change after gcrma()

[yotsawat pomyen]

Dear All, 

I normalised and summarised my data using gcrma() routine and have the 
expression values for each probeset. I now want to do the comparison between two 
classes of the samples (i.e. fold change between the classes). One thing I'm not 
sure is how to compare them because, as I read from the gcrma paper, the 
expression values after the gcrma() routine are log(intensity) after background 
adjustment. 

My question is: Do I have to convert the expression values from gcrma() back to 
raw values by e^(values) before calculate the fold change between the two 
classes that I have? 

Best 

Yot