A recent research has found that the US sees a decline in overall happiness since April 2009 in the midst of increasing Gross Domestic Product.
"After a gradual upward trend that ran from January to April, 2009, the overall time series has shown a gradual downward trend, accelerating somewhat over the first half of 2011," the study said.
The University of Vermont researchers mapped over 46 billion words of Twitter tweets, ranging from "the" to "pancakes", to gauge the relative mood of human groups through an Amazon service, Mechanical Turk.
A group of research volunteers rated their sense of the "happiness" of the ten thousand most common words in English on a one to nine scale.
Averaging their scores, the volunteers rated, for example, "laughter" at 8.50, "food" 7.44, "truck" 5.48, "greed" 3.06 and "terrorist" 1.30.
The Vermont team applied these scores to words they gathered from Twitter.
The tweets provide insights into people's feelings since they contain date, time and occasionally other demographic information.
The study noted though the ultimate aim of public policy is to improve but efforts to measure happiness have been "overshadowed by more readily quantifiable economic indicators such as gross domestic product.
The Vermont scientists hoped that they would be able to infer happiness dynamics "such as individual stability, social correlation and contagion and connections to well-being and health" by following the tweets over long time periods.he research is published in the December 7 issue of the journal PLoS ONE.