— Eric Enge and Stephan Spencer and Jessie Stricchiola and and Rand FishkinEngagement with a website began to emerge as a ranking factor with the release of the Panda update by Google on February 23, 2011 (http://searchengineland.com/google-forecloses-on-content-farms-with-farmer-algorithm-update-66071). Google has access to a large number of data sources that it can use to measure how visitors interact with your website.
Replicated under Fair Use from The Art of SEO by Eric Enge and Stephan Spencer and Jessie Stricchiola and and Rand Fishkin.