Hello All,
I was trying to construct a volcano plot from protein abundance ratio.
So far my understanding goes each ratio( or log_ratio) can have only one
Z score and hence one corresponding P-value to the Z-score.
But in  volcano plots there are multiple P values(along Y axis) for a given
ratio(or log_ratio). How does this happen? Do they pool replicate data with
slightly different mean and std_dev so that Z score and  P-value are
different for
a given ratio.

I've posted a related question in the R-Help list but yet to get any
response:

https://stat.ethz.ch/pipermail/r-help/attachments/20110119/fe1a253b/attachment.pl

http://img402.imageshack.us/i/volcanoi.jpg/

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