Nedra is a consultant, author and speaker who uses social marketing to promote health and social issues for nonprofits and public agencies at Weinreich Communications.
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The elements include:This list would be quite helpful in identifying appropriate bloggers to include in a PR campaign with a social media component. Any one of the indicators of blogger influence by itself would not necessarily provide a full enough picture of whom to target when you need to narrow down what can be resource-intensive outreach. But combine two or more (or all) of these and you will see the degree of influence become clearer.
- Affiliation of blog writer(s)
- Number of links to the blog
- Number of feed subscriptions
- Search engine results position for relevant keyword searches
- Last update
- Industry mentions/lists of top blogs
- Inclusion in Technorati Blog Directory and other online directories
- Discussion Analysis – true discussion or bantering
In English-language, US-centric content, we can generally start the process of identifying potential candidates via search; usually either Technorati, Google or Google Blogs. Then we can refine down into highly linked sites ("most authority" in Technorati lingo).
Social proof can be a powerful marketing tool. If you can get your customers to vouch for your product (or at least make it look like they are) and find a way to advertise it to your potential customers your job as a marketer becomes a lot easier. People don’t want to feel left out and often look to others when making decisions they are unsure of. By being aware of social proof and taking actions to leverage it you can be there when people are looking around to others when trying make a purchase decision.To bring this back to the discussion on influential bloggers, social proof plays a big role in how topics are covered in the blogosphere. When one or more influential bloggers writes about a particular news story or issue, that often sets off a flurry of other posts because the topic has been validated as being important. One influential blogger can provide the social proof that an idea or product has merit, paving the way for many others to adopt it as well.

I think the relevance of the blogger to the audience you are trying to reach is critical. The first question you would need to ask in identifying influential bloggers would be "influential to whom?" Robert Scoble is quite influential, but if you're trying to reach doctors, getting coverage from him won't do much for you. Your point is well-taken, and I will add that to my list for the future.