[Spambayes] understanding high false negative rate

[Jeremy Hylton]

>>>>> "TP" == Tim Peters <tim.one@comcast.net> writes:

  TP> [Jeremy Hylton[
  >> The total collections are 1100 messages.  I trained with 1100/5
  >> messages.

  TP> I'm reading this now as that you trained on about 220 spam and
  TP> about 220 ham.  That's less than 10% of the sizes of the
  TP> training sets I've been using.  Please try an experiment: train
  TP> on 550 of each, and test once against the other 550 of each.

This helps a lot!  Here are results with the stock tokenizer:

Training on <mbox: /home/jeremy/Mail/INBOX 0> & <mbox: /home/jeremy/Mail/spam 8>
 ... 644 hams & 557 spams
      0.000  10.413
      1.398   6.104
      1.398   5.027
Training on <mbox: /home/jeremy/Mail/INBOX 0> & <mbox: /home/jeremy/Mail/spam 0>
 ... 644 hams & 557 spams
      0.000   8.259
      1.242   2.873
      1.242   5.745
Training on <mbox: /home/jeremy/Mail/INBOX 2> & <mbox: /home/jeremy/Mail/spam 3>
 ... 644 hams & 557 spams
      1.398   5.206
      1.398   4.488
      0.000   9.336
Training on <mbox: /home/jeremy/Mail/INBOX 2> & <mbox: /home/jeremy/Mail/spam 0>
 ... 644 hams & 557 spams
      1.553   5.206
      1.553   5.027
      0.000   9.874
total false pos 139 5.39596273292
total false neg 970 43.5368043088

And results from the tokenizer that looks at all headers except Date,
Received, and X-From_:

Training on <mbox: /home/jeremy/Mail/INBOX 0> & <mbox: /home/jeremy/Mail/spam 8>
 ... 644 hams & 557 spams
      0.000   7.540
      0.932   4.847
      0.932   3.232
Training on <mbox: /home/jeremy/Mail/INBOX 0> & <mbox: /home/jeremy/Mail/spam 0>
 ... 644 hams & 557 spams
      0.000   7.181
      0.621   2.873
      0.621   4.847
Training on <mbox: /home/jeremy/Mail/INBOX 2> & <mbox: /home/jeremy/Mail/spam 3>
 ... 644 hams & 557 spams
      1.087   4.129
      1.087   3.052
      0.000   6.822
Training on <mbox: /home/jeremy/Mail/INBOX 2> & <mbox: /home/jeremy/Mail/spam 0>
 ... 644 hams & 557 spams
      0.776   3.411
      0.776   3.411
      0.000   6.463
total false pos 97 3.76552795031
total false neg 738 33.1238779174

Is it safe to conclude that avoiding any cleverness with headers is a
good thing?

  TP> Do that a few times making a random split each time (it won't be
  TP> long until you discover why directories of individual files are
  TP> a lot easier to work -- e.g., random.shuffle() makes this kind
  TP> of thing trivial for me).

You haven't looked at mboxtest.py, have you?  I'm using
random.shuffle(), too.  You don't need to have many files to make an
arbitrary selection of messages from an mbox.

I'll report some more results when they're done.

Jeremy