one of my Colleagues sent me yesterday this amazing presentation with a framework for measuring social media activity. To be honest, I really appreciate the way @ifonlyblog divides metrics into 4 A’s.
Probably I will add something else. It will be interesting to measure how much of the traffic achieved to our website comes from our action or resources (social media plan implementation – community management) to how much is coming as a consequence of Organic or Natural Word of Mouth (E.g. Users who posted our content on their profile).
Basically, we just need to tag (using Google URL Builder) the content we post or the traffic coming from social media ads (E.g promoted Tweets or Facebook ads). This way, we will see on our Google Analytics the source Facebook, Twitter, etc that will represent the Natural and Organic WOM generated because our efforts will be represented differently thanks to the tag included Facebook – Wall post.
After that, social media ROI calculation will be easier and the advocacy as well. Actually, we can measure not only the number of bookmarks, shares, etc. but also the number of clicks coming from earned media (basically free and more valuable).
The only problem is that it needs hard work, time and patience, but you probably will increase your social media campaign effectiveness. Your choice 
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