Twitter Faced SEC Questions on Changing User-Engagement Metrics
bloomberg.com
bloomberg.com
They measure any click on a tweet's body (not a hyperlink) as an engagement; where as an advertiser I define engagement as a favorite, retweet or reply.
You're purchasing time from people that are busy, and productive, and have a life that on the whole it not completely virtualized. Compare that with Facebook and MMPORGs of sorts, and there are some highly successful virtual people who live real lives in mobile homes and shitty apartment complexes. Not to say their overall quality of life is bad, but maybe their balance is off kilter some.