The method created by Peter Dodds and Chris Danforth, a mathematician and computer scientist working in the Advanced Computing Center at the University of Vermont, show that Election Day, November 4, 2008, was the happiest day in four years and the day of Michael Jackson's death, one of the unhappiest.
"The proliferation of personal online writing such as blogs gives us the opportunity to measure emotional levels in real time," they wrote in their study,
Their method to calculate happiness begins with a website, www.wefeelfine.org, that mines through some 2.3 million blogs, looking for sentences beginning with "I feel" or "I am feeling."
"We gathered nearly 10 million sentences from their site," said Dodds.
Then, drawing on a standardized "psychological valence" of words established by the Affective Norms for English Words (ANEW) study, each sentence receives a happiness score.
In the study, a large pool of participants graded their reaction to 1,034 words, forming a kind of "happy-unhappy" scale from 1 to 9. For example, 'triumphant' averaged 8.87, 'paradise' 8.72, 'pancakes' 6.08, 'vanity' 4.30, 'hostage' 2.20, and 'suicide' 1.25.
The sentence 'I feel lazy' would receive a score of 4.38.
"Our method is only reasonable for large-scale texts, like what's available on the WebAny one sentence might not show much. There's too much variability in individual expression," said Dodds.
"It's like measuring the temperature. You don't care where the atoms are. You want to know the temperature of this room or this town. It's a coarser scale.
We're interested in the collective story.
"We were able to make observations of people in a fairly natural environment at several orders of magnitude higher than previous happiness studies," he added.
"They think they are communicating with friends," but, since blogs are public, he said: "We're just looking over their shoulders."
The researchers also apply their method to song lyrics, presidential speeches, and, recently, to Twitter messages.
And they said that it is generally focused on how writings are received rather than what an author may have intended to convey, it does allow them to estimate the emotional state of the blog authors.
"We are thus able to present results of what might be considered a very basic remote-sensing hedonometer," they wrote.
The results are reported in the Journal of Happiness Studies.