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Question: Error bars DESeq or DESeq2 fold change
0
2.2 years ago by
lisa.crossman0 wrote:

Hi,

Some time ago I ran DESeq (one) on a set of data comparing two conditions of growth over 4 biological replicates per each condition.

A collaborator constructed a graph of fold change from that output for approximately 15 genes of interest.

I have a request from a peer reviewer to provide error bars on that graph.

1. Does it make sense to provide error bars on a graph of FoldChange in this way?

2. If so can I generate them for FoldChange either in DESeq or DESeq2 with an R command?  I do have lfcSE from DESeq2 but 2^lfcSE does not seem to make sense, is there a way to generate?

3. Can I get baseMeanA and baseMean B from DESeq2 or would that be identical to the DESeq1 output?

Thanks,

Lisa

modified 2.2 years ago by Simon Anders3.5k • written 2.2 years ago by lisa.crossman0
2
2.2 years ago by
Michael Love18k
United States
Michael Love18k wrote:

Yes you can add error bars to a (log) fold change.

First, I want to say that I always want to see log fold changes, not fold changes, on a plot. The reason is that log fold changes have the property that equal multiplicative changes in either direction (say, up- or down-regulated) cover equal distances on the plot.

Compare:

lfc <- -4:4
par(mfrow=c(1,2))
dotchart(lfc);abline(v=0)
dotchart(2^lfc);abline(v=1)

It's very difficult to see in the second plot that the multiplicative effects to the left of the vertical bar (no change) are equal and opposite effects as those to the right.

Estimated standard errors for the estimated coefficients on the log2 scale are given by the lfcSE column. Yes, you can convert these to fold change errors using this formula: 2^(coef - SE) and 2^(coef + SE).

If you multiple lfcSE by normal quantiles (e.g. qnorm(.025)), you can construct confidence intervals for the coefficients.

DESeq2 is more general purpose that DESeq and so doesn't provide baseMean A and B. You can easily calculate this yourself though. See:

A: DESeq2 baseMean values for each sample

2
2.2 years ago by
Simon Anders3.5k
Zentrum für Molekularbiologie, Universität Heidelberg
Simon Anders3.5k wrote:

Hi

1. Yes, I think error bars do make sense here. The results table returned by DESeq2 contains the columns 'log2FoldChange' with the (shrunken) fold change estimates, and right next to it, the standard errors of these estimates ('lfcSE').  If you add and subtract the standard error to the fold change estimates.you get positions for the upper and lower whiskers of your error bars. Note that these are standard errors, not 95%-CIs, and that there is not correction for multiple testing.

2. You should use 2^(lfc+lfcSE) and 2^(lfc-lfcSE).

Now, this will produce ugly looking asymmetric error bars. My recommendation is to always plot fold changes on a logarithmic scale. After all, you would want a change of 2-fold up (2x) and two-fold down (0.5x) to look the same, though in different directions. Sometimes, people are worried that mathematically less savvy readers find log2-transformed values harder to read or interpret intuitively than raw values. My recommendation here is to nevertheless stick to log-scale axes, but label them in the real scale: Do not label the y axis "log2 fold change" and mark off the equidistant ticks as -3, -2, -1, 0, 1, 2, 3, but label the axis as "fold change" and mark the ticks as 1/8, 1/4, 1/2, 1, 2, 4, 8.

3. The two baseMean values were simply the averages of the normalized counts for the two groups. As DESeq2 is layed out for more general designs, we removed this left-over from the earliest DESeq versions which only allowed for two-group comparisons. If you still need an average over the group, run 'rowMeans' on a suitable subset of columns from 'counts( dds, normalized=TRUE )'.

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2.2 years ago by
lisa.crossman0 wrote:

Brilliant thank you!  I have generated your above figure to discuss with the collaborators

Thanks so much!  I have now generated the numbers for the upper and lower whiskers and the BaseMeanA and BaseMeanB.  I have plotted a few example genes using the lower and upper numbers from the lfc+/-lfcSE as ymin and ymax to ggplot2 geom_errorbar().