"Hi! I'm the author of this column. Thanks for reading it. I'll look forward to interacting here with any comments or questions you might have. One item that I would have included in this article but which came too late before submission: I highly recommend the recent post by Rand Fishkin "Why SEOs Need to Care More About Correlation As Much (or More Than) Causation" http://moz.com/blog/seo-correl... Rand makes a case that an over-fixation on causation metrics (such as "can we prove that our Tweets led directly to sales?) can actually lead to conclusions and consequent actions that may hurt a site in the long run. In contrast, while correlative metrics (and I think most engagement metrics fall in this category) must be approached carefully, they can be read to give indications of bigger trends that may actually be more valuable for the long term health of a business." - Mark Traphagen