Re: Why are BAYES_00 to BAYES_40 scores negative?

On Thu, Jul 03, 2008 at 05:00:13PM -0700, Robert Case wrote:
> I noticed that in many of the messages that got through were hitting the
> BAYES_00 through BAYES_40 rules. I looked at the rules page, and the scores
> for those rules are negative (ranging from -2.599 (eek!) to -0.185). When
> you get to BAYES_50 and higher, the scores turn positive. Also, in many
> instances, the negative BAYES_* scores made the difference between reaching
> the threshold and not.

Yep.

> My question is WHY are those rules negative?

Because they are ham detection rules.

> I went ahead and assigned a positive score for those rules (ranging from
> 0.001 to 0.040), but I figured I had better ask here why those scores are
> negative. I'm figuring there's a good reason, and I don't want to shoot
> myself in the foot.

Bayes provides a probability of a message being spam. Therefore: 50% is "not sure either way", 0% is "not spam", 100% is "definitely spam".

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