[R] Log(2) values to log(10) values

[James W. MacDonald]

Srinivas Iyyer wrote:
> Dear group, 
>  I am using justRMA in bioconductor to get expression
> values.  Now I computed fold changes.  the fold
> changes i get are log2 values.  
> 
> How can I convert these to log10 values to see them as
> actual fold change values. 

First, a bit of etiquette. It is considered impolite to post the same 
question to more than one listserv. Second, although this is not a 
BioC-specific question, that is probably a better place to ask.

To answer; log10 values will *not* give you actual fold changes. These 
will be the same as log2, to a multiplicitive constant. You want to 
convert back to the natural scale e.g., 2^FC, where FC = your fold changes.

Also note that you compute fold change on the log scale by subtraction, 
not division.

HTH,

Jim


> 
> thank you.
> 
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-- 
James W. MacDonald
Affymetrix and cDNA Microarray Core
University of Michigan Cancer Center
1500 E. Medical Center Drive
7410 CCGC
Ann Arbor MI 48109