Matt Hurst has an interesting posting over at Data Mining about the correlation of number of readers and number of inlinks on a given blog or site. He polled a random selection of Feedburner-hosted feeds using the Feedburner awareness API, which provides information about how many subscribers a feed has.

Not surprisingly, he found a rather weak correlation between subscribership and inlinks. This is because of the well-documented participation ratio in social environments that draws on the Pareto principle. Ross Mayfield explains:

In Wikipedia, 500 people, or 0.5% of users, account for 50% of the edits. This core community is actively dedicated to maintaining an open periphery. Part of what makes Flickr work isn't just excellence at low threshold engagement, but the ability to form groups.

While many may listen, few act frequently. But as Ross's own software, the Socialtext wiki, demonstrates, when you give members of a group meaningful context, they participate more. (Disclosure: I'm on the board of advisors at Socialtext.) Readership, therefore, will not strongly correlate to inlinking by those readers, because there are other factors that motivate greater social participation than simple consumption.

I agree, however, with Matt that there the opportunity to influence is an important factor to consider. This is a familiar concept for many marketers, because it is reach repackaged for a social world. There is less control of the inventory of influence opportunities—or, more simply, "impressions"—when both the number of channels of communication and volume of options have increased exponentially. A number of factors to consider:

• Subscribers are not necesssarily readers. I believe Matt should discount the number of readers to account for the percentage of subscribers who never get to the posting. This would increase the R2 correlation.
• Context, which is what we are particularly interested in at BuzzLogic, is critically important to converting opportunity into influence. We look at the frequency with which blogs and media participating in a conversation deal with the topic in question. This is much more than a matter of counting keyword frequency.
• Linkless or unattributed influence must be measured, as well. Inlinks are only one way we acknowledge a source of ideas. We've found that some sites accelerate individual topics more frequently, presumably because when these authors speak they are treated as more authoritative than others. Because of this a blog with a very low readership deeply interested in a specific topic can be tremendously influential without getting many inlinks. Just consider how frequently we quote others without naming them or attributing the quote to the wrong person, yet the source of the idea has still had influence on the ideas expressed.

Matt's onto something. The first thing I'd focus on is correcting for non-reading subscribers. Reach, however, is only one step in linking expression and influence. Greater reach does not necessarily translate into influence, it's not a causal relationship.