I don't think anyone will argue that Slashdot moderation is good. Better than nothing? Yeah, sure. I use the higher numbers to filter out the the best comments. That works somewhat, but not well.
I guess the purpose of moderation is in question. My childish gut reaction is a reward system. Good post, here's a karma point, or "kudos". Bad post, shame on you, here's a slap. I think that would explain the general tendencies. However, when I actually *read* article comments, I use the moderation totals to weed out the best comments, unless I want to read what everyone has to say. IIRC, that was Taco's original intention.
The most disturbing thing for me is the ratio of comments in each number. +2 are for people with a quickie mod. Mods happen a lot, and many comments will be modded. Does half sound good? +3 is already pushing it, this is a double mod. In other words, a serious comment. Whatever the ratio of +2 to +1, +3 should be even less in relation to +2. +4 should be the same, and +5, the ultimate mod, should have next to nothing in it.
Here's the breakdown excluding -1.
# AMT Twd Lwd Per Lwdp
0: 3161 0000 0000 00.0 00.0
1: 2268 0893 0893 71.7 28.7
2: 0919 2242 1349 29.0 43.4
3: 0144 3017 0775 04.5 24.9
4: 0074 3087 0070 02.3 02.2
5: 0059 3102 0015 01.8 00.4
# - Moderation number.
AMT - Amount of comments.
Twd - Total amount of comments weeded out. (Amt - 3161)
Lwd - Amount of comments weeded out this level. (Last level's AMT - AMT)
Per - Percentage of total comments. (AMT / 3161)
Lwdp - Percentage this level weeded of total. (Lwd / 3102)
+2 cuts out most of the comments. +3 is good too, it further cuts the comments in half. +4 already, however, is dissapointing. It only weeds around two percent of the total comments or only half of the last level's. And +5 is a joke, weeding less than half a percent,a dn staying nearly the same as the last level.
I think a study should be done on many stories. To see the general tendencies, and when moderation works. In popular stories, past +3 it really doesn't, though there must be a way.