Measuring the emotional content of tweets as
reflected by the presence of positive or negative words, scientists assessed the "subjective well-being" of the users through their tweets. The result? "It turns out that Twitter users are
preferentially linked to those with whom they share a similar level of general happiness," psychologist Johan Bollen of the University of Indiana tells New Scientist.
Bollen and his colleagues don't yet know why tweeters behave this way, although he suspects that the emotions expressed even in short tweets have an infectious quality, lifting peoples' spirits or filling them with gloom, depending on what they read.
Connected: The Surprising Power of our Social Networks by Nicholas Christakis and James Fowler, explains the "birds of a feather" effect. People are attracted to like people. Based on the Farmingham heart study data, people with similar lifestyles and outlooks are networked together.
This makes complete sense. Physical relationships are frequently based on proximity. Virtual relationships aren't limited by that barrier so connecting with like minded individuals with similar life philosophies is one of the benefits from social networking tools like Twitter. People have always sought out other individuals that validate their values; positive or negative. So now birds of a feather can be classified as Chirpers or Squawkers depending on their slant.