Genuinely if an alternative "lay definition" had taken root, I took a look around, and...
The "professional" definition looks like a "marketing numbers" game, since their "false positive" rate totally obscures the real situation and inflates "the number" to the most flattering level (use the biggest possible number in the denominator).
So the marketing guy says: There is a 0.1% "false positive" rate, meaning for a total of 1000 messages we handled, we erroneously rejected one 1 legit message as spam.
Is their "false positive" rate a quality or accuracy indicator? no
The nasty questions they won't answer:
1. How many of the accepted messages were really spam?
2. What is the rate of ( false positives / rejected messages )?
The preceding number is the one that interests mail admins have to deal with.
That "false positive rate" may be the conventional, professional number but it's a useless number because it does not say how accurate our reject/accept decisions were. It's marketing fluff.
Decision: is a msg spam?
If yes, reject
If no, accept
1. I reject 1000 messages as spam (true positives), but 5 of them were falsely rejected (were legit). So that's a 0.5% false rejects. aka false positives. ie, I screwed up on 0.5% of my rejects.
2. I accept 1000 messages as legit (non-spam), but 8 of them are really spam. So that's 0.8% "false negatives", ie, false non-spam.
So when an Imail/Declude/Sniffer user adds IMGate, he gets of the total rejects, 97% rejected by IMGate, and other 3% rejected by Sniffer.
A test lab ( or testing kit mfr) advertises:
"We just tested 100k people for monkey pox and had one false positive, we are great, so use our lab / buy our stock"
In between the lines, what really happened was that in 100k people, 10 tested positive for monkey pox, and 1 of those 10 really didn't have monkey pox. So the decision: "this person has monkey pox" was wrong (false positive) 10% of the time. My observation: your lab / your testing kit sucks.
The totally separate "false negative" evaluation is: of the 99,990 decisions "this person doesn't have monkey pox", how many really did have monkey pox (false negative)?
Len
_____________________________________________________________________ http://MenAndMice.com/DNS-training: New York; Seattle; Chicago IMGate.MEIway.com: anti-spam gateway, effective on 1000's of sites, free
To Unsubscribe: http://www.ipswitch.com/support/mailing-lists.html List Archive: http://www.mail-archive.com/imail_forum%40list.ipswitch.com/ Knowledge Base/FAQ: http://www.ipswitch.com/support/IMail/
