p-value<0.05 for a gene with zero counts?
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@andrebolerbarros-16788
Last seen 9 hours ago
Portugal

Hi everyone,

I was performing a comparison using DESeq2. Considering it is relevant for the case, I used a code I found here (DESeq2 baseMean values for each sample) to find the mean counts for each condition.

So, looking at a gene where both groups have zero counts, I obtained a significant p-value (quite small even, 5.7E-6). Since I had a warning about convergence, I also checked and it did converge.

Is this possible? I understand that the independentFiltering maintains the gene, since it has reads for other conditions but, considering the counts, it should be at least non-significant no?

The code is rather straightforward:

baseMeanPerLvl <- sapply( levels(dds_sub$CellType), function(lvl) 
      rowMeans(counts(dds_sub,normalized=TRUE)[,dds_sub$CellType == lvl, drop=F] ) )

resultsNames(dds_sub)
res1<-results(dds_sub,name =  "CellType_Neutrophils_vs_Eosinophil", alpha = 0.05)
res1<-lfcShrink(dds_sub,coef = "CellType_Neutrophils_vs_Eosinophil", type = "apeglm",res = res1)

Thanks in advance

DESeq2 • 547 views
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@mikelove
Last seen 59 minutes ago
United States

Can you use contrast instead of name? This should resolve it.

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It indeed solved the problem, now the genes in question get a p-value of 1 and log2FC. However, what does this means for lfcshrink, should I keep the usage of coef for apeglm?

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Yes, you can keep use of coef in apeglm.

And note that in apeglm you can specify svalue=TRUE or an lfcThreshold even if you want to find a set of genes with large posterior LFC.

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