Go Back   SEQanswers > Applications Forums > RNA Sequencing

Similar Threads
Thread Thread Starter Forum Replies Last Post
EdgeR cpm values after batch effects danielfortin86 Bioinformatics 4 08-25-2013 09:12 PM
[EdgeR] exactTest dispersion="common" syintel87 Bioinformatics 0 05-23-2013 06:12 PM
Help with edgeR kvk727 Bioinformatics 1 01-21-2013 01:31 PM
edgeR wangli RNA Sequencing 4 04-19-2012 06:58 AM
edgeR Puva Bioinformatics 2 05-19-2011 09:04 AM

Thread Tools
Old 07-31-2013, 04:00 AM   #1
Location: Copenhagen, Denmark

Join Date: Dec 2012
Posts: 17
Default CPM in EdgeR - before and after exactTest

I have normalized my RNAseq read counts in EdgeR. If I try to look at the normalized data:

total=cpm(w, normalized.lib.size=TRUE)

And specifically the CPM values for my cell line 1 (in triplicates) for the gene Hspa5

7492.944 6750.397 5727.190

If I find the fold change between cell line 1 and my control cell line 2 I get:

3.409239 3.399253 2.910913

So by this very basic test I find that a fold change of about 3.3 fold is found between my two cell lines

Then I use EdgeR to find the same
et <- exactTest(w, pair=c(13,1))
logFC logCPM PValue FDR
Hspa5 1.80454 12.11638 2.519341e-65 4.262793e-63

FC = exp(1.80454) = 6.077175
CPM = exp(12.11638) = 182842

So after EdgeR has made the comparison the CPM value is suddenly 27x higher and (more importantly for me) the fold change is 2x higher. Is there someone out there that can explain this difference for me?

I have read this thread ( stating that log(CPM) is actually taking into account the estimated dispersions and the library sizes... but 27x difference? and why the 2x difference in the fold change?

Which of the 2 results would you state in a table showing your RNAseq results in a publication?
Kaas is offline   Reply With Quote

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

All times are GMT -8. The time now is 07:29 AM.

Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Single Sign On provided by vBSSO