Twitter is being used to measure the state of mind of Americans at any given time, day, or place - by means of a Mood Map, created by researchers at Northeastern University in Boston.

The "map" uses a psychological word-rating system to analyse key words in Twitter messages as happy or sad.

People are happiest in the morning and in the evening, with happiness peaking on Sunday morning and dipping on Thursday night, they found. Tweeters appeared most gloomy at mid-afternoon, shifting to better moods in the evening.

Not surprisingly, people appeared happier at weekends, with residents of California, Miami and southern states among the most content, they learned.

A colourful time-lapse video on the website http://www.ccs.neu.edu/home/amislove/twittermood/ shows the happy moods pulsating from the US east coast to the west coast and back again.

The researchers are the first to admit the findings are not terribly scientific - Twitter users tend to be tech-savvy, live in large cities and are a fraction of the total population - but according to the results, they have potential as a tool for providing real-time analysis of critical issues.

"Even though individual tweets are pointless to anyone besides your followers, in aggregate there is a lot of meaningful information that can be an instrument to see how people feel about things, whether it's public reaction to a politician's speech or a consumer attitudes about a brand," said Sume Lehmann, one of the researchers.

Lehmann and others created maps based on the location of the messages with the key words and the general moods they evoke.

The map could be useful not only to collect public opinion but to mobilise users quickly, such as in a drive for emergency relief donations.

"The potential there is tremendous, on both an individual and societal level," said Johan Bollen, a computer scientist at Indiana University. - Reuters