Dear Bjorn,

Thanks so much for your reply.

Yes, I understand that the initial peptide probability will be
adjusted to take into account of sibling peptides -> nsp adjusted
probability. I was referring to the initial probability itself. And
we've possibly just found out why through some tests.

Our Protein Prophet step was done with a number of input files, from
Inter Prophet. Although Inter Prophet is meant to combine results
before running them into Protein Prophet, we are unable to combine all
the results as there were too much data. Hence, results were split
into a number of Inter Prophet files. When these files were processed
in a single Protein Prophet run, peptides that were only found in one
of the Inter Prophet files were given a lower initial peptide
probability.

When only the particular Inter Prophet file was selected for a Protein
Prophet run, the initial peptide probability reported for the peptide
is correct.

Cheers
Eric


On Nov 13, 11:14 pm, Bjorn <[email protected]> wrote:
> Hi Eric,
> If I'm not mistaken, the ProteinProphet "re-evaluates" the peptide
> probabilities based on the number of sibling peptides 
> (NSP).http://www.proteomecenter.org/2010.OCT/Seattle%20Course%20Pack.pdf
> (pages 92-93 answer your question)
>
> Hope this helps,
>
> Cheers,
> Bjorn

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