Hi,

Here's a short talk I gave years ago for a user meeting on X!Tandem:
www.proteomesoftware.com/XTandem_edited.pdf

Pages 11-14 discuss how the e-value is calculated.  What do you mean
exactly by data set/sequences?  The e-value is not dependent on the
number of spectra in a data set as individual spectra are not scored
together (although PeptideProphet will have a harder time trying to
make sense of small data sets).  The e-value can be database dependent
and it may not work well for a 100 sequence FASTA database if you're
employing high-mass accuracy peptide selection criteria.

Best, Brian


On Oct 20, 3:24 am, dhirendra <[email protected]> wrote:
> hi,
>  can anyone provide me detailed explanation about how the X!tandem e-
> value is calculated and how good is it for small dataset of say 100
> sequences?

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