Limma Analysis, BH Correction - adj. P-value all the same value
0
0
Entering edit mode
8.1 years ago
Cale Reid • 0

Hi All,

I'm new to R and Limma, so apologies in advance for my naivete.

I'm analyzing some microarray data, and after applying the BH correction w/ topTable, I end up with a list of genes where the adj. P-value is apparently all the same. How do I interpret that? The P-values (unadjusted) vary significantly, but the ad. P-value for each gene is the same number (0.2800681 in my case).

I also note that some of my top results are labeled as normgene->intron (aka not real genes). Could this be the issue? I used the oligo package for initial processing of my data.

Any guidance would be much appreciated.

R limma • 7.2k views
ADD COMMENT
0
Entering edit mode

If you make a histogram of the unadjusted p-values, what does the graph look like? Just upload that image somewhere and provide a link.

ADD REPLY
0
Entering edit mode

Hey Devon. Thanks for your help. A histogram of the unadjusted P-values looks like this: http://imgur.com/SBJf1zu

ADD REPLY
0
Entering edit mode

You'll need to show all of the genes, not just the top 100.

ADD REPLY
0
Entering edit mode

Done: http://imgur.com/OpO1eiK

top_100 is a bit of a red herring - the 100 refers to my experimental condition, not the # of genes, but yeah - I definitely hadn't included all genes in the histogram before

ADD REPLY
0
Entering edit mode

Wow, that looks like you should have some significant genes after correction. Do you get the same results if you manually run p.adjust() on the p-values?

ADD REPLY
0
Entering edit mode

Here's what my table looks like after using p.adjust manually: http://imgur.com/GXXmpdw

P-value and adjusted p-value are from limma. The actual_adjusted p-value is from taking the limma provided p-value and using p.adjust with the BH correction.

Any thoughts? I can't figure out why they'd be different even though supposedly both limma and p.adjust are using BH.

ADD REPLY
0
Entering edit mode

That's by far the craziest (bioinformatics related) thing I've seen this week. I'm pretty sure limma is even calling p.adjust() internally, so I have absolutely no clue why it's giving you those results. You might post this over on the bioconductor site, where Gordon Smyth (the limma author) can have a look.

ADD REPLY
0
Entering edit mode

I posted on the bioconductor website - thanks again for your help. This is mystifying my partner and I as well so hopefully someone will know what's up!

ADD REPLY
0
Entering edit mode

Would have been helpful to provide the link to your post on bioconductor's webpage.

ADD REPLY
0
Entering edit mode
ADD REPLY

Login before adding your answer.

Traffic: 2713 users visited in the last hour
Help About
FAQ
Access RSS
API
Stats

Use of this site constitutes acceptance of our User Agreement and Privacy Policy.

Powered by the version 2.3.6