edgeR, "DGELIst" function, "group" parameter

[David [R]]

Hi,

I am using edgeR for some RNASeq analysis. My question concerns the DGEList function and its "group" parameter. I realized that, whether doing group=mydesignfactor or group=rep(1,ncol(counts)), the cpm numbers that I get after
counts.TMM <- calcNormFactors(counts.DGEList)
cpm.TMM=cpm(counts.TMM, normalized.lib.sizes=TRUE)
are strictly identical in either case. The only difference between both ways is that the counts.TMM$samples$group column duly reflects what I put in in "group".

Is this normal? What is it that I am missing? Is the "group" nevertheless taken into account on the subsequent estimateGLMCommonDisp, estimateGLMTrendDisp, estimateGLMTagDisp, glmFit, glmLRT etc.?

Thanks in advance for your help.

Best,

David Rengel

[dpryan]

There's no reason that cpm should be dependent upon your experimental design (in fact, it shouldn't be). The various GLM function pay attention to the design, since that's where it's important.

[David [R]]

Hi dpryan,

THanks for your reply. Yes, that is right. My only only doubt came from de fact that if normalized.lib.sizes=TRUE, then the cpm are calculated using the normalization factors, which I thought were somehow dependent on your experimental design, but it seems I was mistaken.

David

[dpryan]

Correct, normalization factors are independent from experimental design.

[David [R]]

Thanks a lot!