Problem in finding NB dispersion for my HiC datasets
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@manjulathimma-11250
Last seen 4.9 years ago

Hi Aaron,

I have two datasets of HiC experiment on , one control and one sample. I am trying to use diffHiC to find differential interaction between them.

While going through the user manual and following the instructions, I got stuck up at Modelling biological variablility.

design <- model.matrix(~factor(c("hepg2","ago1")))
> colnames(design) <- c("HepG2","Ago1")
> design
HepG2 Ago1
1     1    1
2     1    0
attr(,"assign")
[1] 0 1
attr(,"contrasts")
attr(,"contrasts")$factor(c("hepg2", "ago1")) [1] "contr.treatment" > y <- asDGEList(data) > y$offset <- nb.off
> y <- estimateDisp(y,design)
Warning message:
In estimateDisp.default(y = y$counts, design = design, group = group, : No residual df: setting dispersion to NA > y$common.dispersion
[1] NA
[,1]       [,2]
[1,] 0.5439510 -0.5439510
[2,] 0.5342466 -0.5342466
[3,] 0.5398196 -0.5398196
[4,] 0.5375195 -0.5375195
[5,] 0.5434533 -0.5434533
[6,] 0.4076305 -0.4076305

Why am I not able to see common.dispersion?

Best,

Manjula

diffhic • 865 views
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@james-w-macdonald-5106
Last seen 5 hours ago
United States

The short answer is that you can't estimate the dispersion if you don't have any replicates.

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Also see the recommendations in section 2.11 of the edgeR user's guide, on what to do when you have no replicates.

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If dispersion cant be estimated, then how do I create fit object to take next step of 'testing for significant interactions'. Is there any work around for handling samples without replicates?

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See points 2 and 3 of section 2.11. However, these are only stop-gap solutions; the correct fix is to perform the experiment again to obtain a set of replicates. Never mind dispersion estimation, it's just good science - the only way to know if your result is reproducible is to do it again. You'll also get more power to detect differences when you have more samples.