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Question: DESeq2 - Effect of DDS Import of All vs Select Conditions
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gravatar for pvd2107
9 months ago by
pvd21070
pvd21070 wrote:

Hi Everyone,

We've recently completed an RNASeq experiment with 35 samples and 10 different conditions. Almost all of our biological questions are about pairwise comparisons between two of these conditions. 

As of now, my workflow has been to import all of the samples as follows:

dds <- DESeqDataSetFromTximport(txi.salmon, sampleTable, ~condition)
dds <- dds[ rowSums(counts(dds)) > 10, ]

nrow(dds) -> 33,270

After I've done this, I've ran DESeq on the enitre dds dataset:

dds <- DESeq(dds)

I've then proceeded to run results on the pairwise comparison of interest:

YCNT <- results(dds, contrast = c("condition", "YB6CNT", "YBJCNT"), alpha = 0.05, lfcThreshold = 1)

In this instance, I find very few significant differences using the log2 and padj thresholds (which is not that surprising since this is a control condition comparison)

> table(YCNT.05$padj < 0.05)

FALSE  TRUE 
33072    24 

My question is, if I'm interested in just this comparison, is there any difference in how the model runs if I were to only import the samples corresponding to these two conditions to begin with, as opposed to importing all 35 samples and then running the pairwise results contrast?

For example, I could imagine that the initial DDS filtering would return less rows with rowsum >=10 and that might make the FDR less strict. I'm not sure if that is accounted for in the model, but was just curious if one approach is more appropriate than the other.

Thanks a lot.

Paul

ADD COMMENTlink modified 9 months ago by Michael Love20k • written 9 months ago by pvd21070
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gravatar for Michael Love
9 months ago by
Michael Love20k
United States
Michael Love20k wrote:

This is one of the frequently asked questions in the DESeq2 vignette.

ADD COMMENTlink written 9 months ago by Michael Love20k

sorry about that, thanks!

ADD REPLYlink written 9 months ago by pvd21070
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