The scientific study "Pulse of the Nation: U.S. Mood throughout the Day Inferred from Twitter" [ccs.neu.edu] illustrates the varying mood in the U.S., as inferred after analyzing over 300 million tweets that were created over the course of the day. Various density-preserving cartograms and a time-animated video were produced to capture important large-scale trends.
The researchers analyzed all public tweets posted between September 2006 and August 2009, and filtered those whom orginated from a US location and those that contained words included in the psychological word-rating system called Affective Norms for English Words, resulting in a collection of 300 million tweets. Through a natural language processing algorithm called Sentiment Analysis, each tweet was assigned a mood score based on the number of positive or negative words it contained. Out of the resulting data, they then calculated the average mood score of all the users living in a state hour by hour which formed the basis of a series of time-varying mood maps.
One of the interesting patterns shows how the West Coast mood follows the same pattern as the East, with a 3-hour time-zone delay, indicating that Each Coast experiences the same time-dependent swings. Weekends were observed to be happier than weekdays. The peak in the overall tweet mood score is observed on Sunday mornings, and the trough occurs on Thursday evenings.