"This post from Mark Schaefer of Social Media Today discusses how he went about discovering if his blog had any impact. Quite simply, he contacted people who had left comments on his blog and spoke with them directly. He was able to discover a very real impact he had on readers this way.
If you blog as part of your Extension work and want to document impact a great place to start is with your commenters. You have a couple of options - you can create a survey to send to them or you can contact them individually and have an informal conversations. We often measure engagement on blogs through the number of comments but this offers a way to go beyond basic engagement metrics and find out how you are really impacting your audience. This also gives you a way to discover more about your audience. Who are they and why do they read your blog out of the millions of blogs on the web. How did they discover you? Have they learned anything or changed practice based on your blog?
Let me know if you have other ways you have dug deeper into evaluating your blog."
Via Sarah Baughman