I am late to this, but I still find it fascinating that they were able to produce this study using just tweets. But they did, and as it says in the NYTimes.com, our Moods on Twitter Follow Biological Rhythms. Quote:

However grumpy when they wake up, and whether they stumble to their feet in Mumbai, Mexico City or Minnetonka, Minn., people tend to brighten by breakfast time and feel their mood taper gradually to a low in the late afternoon, before rallying again near bedtime, a large-scale study of posts on the social media site Twitter found.

What I f