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Re: False Positive -was- RE: [Asrg] Fwd: Returned mail: see transcript for details

2003-04-02 13:52:32
On Tue, Apr 01, 2003 at 02:18:34PM -0500, Liudvikas Bukys wrote:

I slightly prefer the terms accept/reject over negative/positive.

PROPORTION DEFINITION:

I think that a 2x2 matrix is most straightforward presentation:

      {accept,reject} x {ham,spam}

      accept  reject  total
ham   TA      FR      NHAM = TA+FR
spam  FA      TR      NSPAM = FA+TR
total TA+FA   FR+TR   NTOTAL

and the most helpful intuitive proportions (I think) would be
FRp = FR/NHAM and FAp = FA/NSPAM.

Numbers will ALWAYS be dependent on a particular corpus.

However, I think that the definitions above will be stable
(measuring classifier quality, not corpus composition) over
a wide range of ham-spam ratios.  Using FR/NTOTAL or FA/NTOTAL
will be dominated by ham-spam ratio of the test set, obscuring
the performance of the classifier, making results unnecessarily
corpus-specific.

  This is exactly correct, IMHO.

  Your matrix is a flipped version of the matrix I just presented in
proposing the FP/FN calculations to be used for the "dSpam" measure.

  -- Clifton

-- 
     Clifton Royston  --  LavaNet Systems Architect --  
cliftonr(_at_)lava(_dot_)net

  "If you ride fast enough, the Specialist can't catch you."
  "What's the Specialist?" Samantha says. 
  "The Specialist wears a hat," says the babysitter. "The hat makes noises."
  She doesn't say anything else.  
                      Kelly Link, _The Specialist's Hat_
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