I’m starting to write my book, The New Influencers, and I’ll occasionally post notes and chapters for your perusal and comment. This is for a chapter on measuring influence:

Nielsen BuzzMetrics monitors 30 million blogs yielding 500,000 to 1 million posts a day. The service provides marketers with insight into what’s being discussed in the blogosphere, as well as what’s being said about their products. Links are the best indication of a blog’s influence, says Natalie Glance, Ph.D, a senior research scientist. “Readership is a good proxy for influence,” she says. “The more readers a person has, the greater their reach and the more likely they are to influence somebody in mainstream media and reach beyond the blogosphere.”

Nielsen mainly looks at links. It crawls the blogosphere daily for new posts and harvests links to other blogs. Proprietary technology separates blog posts from, say, newspaper articles, and filter out disruptions like spam blogs and link farms.

Not all links are treated the same. Blogroll links, for example, aren’t counted because they’re persistent and most bloggers don’t scour their blogrolls every day. The correlation between links and readership is elusive but measurable. To establish the relationship, Nielsen BuzzMetrics found sites that list traffic meters and then correlated link activity to those sites. The truth: the more active links a site has, the more traffic it gets.

While links are important indicators of influence, they can be situational, Glance says. Entertainment and celebrity sites, for example, don’t generate much cross-linking activity, while tech sites are notable for having a copious number of links. That’s where comments are figured into the equation. Sites that don’t generate many links often spark a lot of comment activity. Gadget blogs have a lot of both.

Influence in different markets is, therefore, different. Link counts are relative to the overall link activity in a market. In other words, a site that doesn’t generate links or comments may still be influential if its competitors don’t either. That also factors into the BuzzMetrics equation.

Glance acknowledges that influence measurement in the blogosphere is still primitive, and Nielsen BuzzMetrics, like other measurement firms, is refining its craft. One idea is to categorize blogs by topic and measure their metrics against each other on the assumption that overall activity is relative to the topic being discussed. Another is to weight different blogs differently, so that a link from an A-list blog is assigned more importance than one from a lesser-known outlet. Mainstream media is also not currently figured into the equation.. The service can measures links from blogs to newspaper articles, but not the reverse.

Two things are clear, Glance says. One is that the blogosphere be a very different place without mainstream media. “There’s more linking to mainstream media in the blogosphere than there is to other blogs,” Glance says. Mainstream media is the principal source of information upon which bloggers comment. Another truism is that blogs about sex, movie stars and Parris Hilton get a disproportionate amount of traffic. “The most popular stories in the blogosphere aren’t necessarily the most important ones,” she says.

Nielsen BuzzMetrics’ BlogPulse is an excellent window on the blogosphere with a lot of interesting metrics and search tools. If you’re a Technorati fan, check it out because you will find new and interesting tools there.