I’ve been indicated a few places saying a third of blogs are spam. Someone came up with this by me saying we’ve axed around 800,000 splogs on WordPress.com, and looking at our number of blogs, which is 2.5m.

As for percentage of the total blogosphere, reported by Technorati as north of 100 million, which are splogs, I’d say the number is much higher – probably 80%. This isn’t as bad as it sounds, I just think spammers are very effective at creating hundreds of thousands to millions of blogs, they tend to stick around, and I feel like Technorati’s number doesn’t doesn’t adequately scrub these out.

While I’m making data-less estimates, I’d say there are about 25-30 million non-spam blogs, and about 8-14 million of those are active in terms of getting traffic or new posts. You could cover a meaningful portion of the blogosphere by just indexing 4 or 5 million blogs.

Splogs and blogger attrition are two problems no one really talks about, but that’s okay because I don’t think either is hindering anyone’s growth as measured by metrics that matter, like pageviews or uniques. (Though many of the services supporting so many splogs must have an inordinate amount of resources devoted to them.)

See also: Blog Ping and Spam Statistics, WordPress.com February wrap-up.