DESeq -padj
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Dawei Li ▴ 50
@dawei-li-4693
Last seen 7.1 years ago
Dear Simon Anders: I am using your DESeq package for data analysis. I have one little quetion regarding the package: In the manual, it is said that padj controls the FDR value. Can I simply call padj as FDR?   My clients want the FDR value. I tell them padj is the FDR value. [[alternative HTML version deleted]]
DESeq DESeq • 4.7k views
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Simon Anders ★ 3.7k
@simon-anders-3855
Last seen 14 months ago
Zentrum für Molekularbiologie, Universi…
Hi Dawei On 2011-06-13 14:56, Dawei Li wrote: > Dear Simon Anders: > > I am using your DESeq package for data analysis. > > I have one little quetion regarding the package: > > In the manual, it is said that padj controls the FDR value. Can I simply > call padj as FDR? > > My clients want the FDR value. I tell them padj is the FDR value. > The 'padj' values is what your clients want, however they and you are incorrect in calling them FDR values. An individual test (i.e., a gene) never has an FDR value, it has an adjusted p-values. (Exception: so-called local FDRs, which I am not using here.) The definition of a "p value adjusted for FDR control" is: If one takes all tests (genes) with an adjusted p value below a threshold f, then the list of these genes contains (in expectation) at most a proportion f of false dicoveries, i.e., thresholding adjusted p values at f controls the false dicovery rate (FDR) at f. Hence, the term "FDR" refers to the threshold you cut the adjusted p values at, not to the adjusted p values themselves. Simon
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Dear Simon - Further to your comments on FDR and padj: does that mean that a frequency histogram of padj is invalid as these values refer to a threshold rather than individual values? What I mean is: a histogram of FDRs would be invalid as each FDR value only applies to the list of genes above it in the ranked list (or so I understand) and not to the gene itself. Therefore, does this caveat also apply to padj? 

Regards,
Matt Arno

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