Question: Correct usage of tximport counts in edgeR without offset matrix.
7 weeks ago by
ttekath • 0
ttekath • 0 wrote:
first I want to thank the authors of tximport and edgeR for their very informative vignettes – these are super helpful.
Nonetheless I have two small questions still bugging me:
- If I am using the method “bias corrected counts without an offset” from the tximport vignette to use my tximport counts in edgeR: Would i still need to execute the edgeR
As far as I understand it would not be necessary, because the usage of "lengthscaledTPM" in tximport should have already corrected for library size differences, correct?
Here is an exemplified rundown:
txi <- tximport::tximport(files = files, type = "salmon", tx2gene = tx2gene, countsFromAbundance = "lengthScaledTPM" ) dge <- edgeR::DGEList(counts = txi$counts, group = grouping_variable) design <- model.matrix(~batch_variable + group , data=dge$samples) #filter low expressed genes keep <- edgeR::filterByExpr(dge, design) dge <- dge[keep, , keep.lib.sizes=FALSE] #necessary? dge <- calcNormFactors(dge, method = "TMM") dge <- edgeR::estimateDisp(dge, design, robust=T) #....
- Is one of the methods "bias corrected counts without an offset” and “original counts and offset” recommended over the other? Because the
cpm()method of edgeR is not taking the offset-matrix into account, therefore it is much easier to get log-transformed CPM for plotting (e.g. heatmaps) without using the offset approach.
Thanks in advance.
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