Question: Limma p-values, fdr and classifyTests
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14.8 years ago by
Matthew Hannah940 wrote:

Hi,

I'm using Limma and have some questions related to p-values and gene selection.

Looking in the classifyTests help I noticed "The adjustment for multiple testing is across the contrasts rather than the more usual control across genes." There is also a multiple testing procedure for the topTable function but this appears to give a different result (fewer sig. genes) - is this the more usual control across genes? Why are they different? Is it possible to take both into account?

Basically I'm not just interested in the top 50 genes, I'd like to identify all 'significant' changes. I thought the output from classifyTestsP (0.01, fdr) would be good but this doesn't account for across gene multiple testing. Is there an easy way to get this output rather than calling topTable (if the fdr is across genes?) for all genes?

classifyTestsF could be useful as I'm looking at a treatment effect on different lines. However, again there is no account of across gene multiple testing. Is there any possibility to do this?

Also, all this talk of p-values but there is a note saying they are nominal. How far does this hold true - do you always have to select a cut-off based on some criteria (eg:control genes) or is there a way they can be applied quantitatively?

Finally is it ok to pass an eBayes fit to topTable? What's the difference compared to toptable?

fit <- lmFit(esetgcrma, design)
con.fit <- contrasts.fit(fit, cont.matrix)
ebfit <- eBayes(con.fit)


Thanks alot,

Matt

limma • 468 views
modified 3 months ago by Gordon Smyth37k • written 14.8 years ago by Matthew Hannah940
Answer: Limma p-values, fdr and classifyTests
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3 months ago by
Gordon Smyth37k
Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia
Gordon Smyth37k wrote:

Just use decideTests instead of classifyTests. The latter does not adjust for multiple testing across genes and is not intended to be called directly by users (as the help page says). decideTests does everything and calls the other functions as needed.