Mood poll highlights work stress
All over the world, people are waking up and going to bed happy. It's the bit in-between that is the problem, a study suggests.
Scientists used the micro-blogging site Twitter to monitor mood changes in 2.4 million people from 84 countries.
Analysis of more than five million "tweet" messages delivered at different times of the day revealed a similar pattern regardless of location and culture.
Over a two year period from February 2008 to January 2010, people in America, Europe, Africa and Asia demonstrated two notable peaks of positive attitude.
One was at the start of the day, relatively early in the morning, and the other at the end, near midnight.
In contrast, negative mood was lowest in the morning and rose during the day to a night-time peak.
Tweeters were also more cheerful at weekends, according to the findings published in the journal Science.
The results highlight the "refreshing" power of sleep but also show how work stress can dampen the spirits, say the researchers led by sociology professor Michael Macy, from Cornell University in New York.
However, the pattern also indicated that sleep and the biological clock had an important influence regardless of whether people were working or not.
No correlation was found between absolute levels of daylight and mood. But people became less positive with approaching winter as days shortened, and more positive as they lengthened in the spring.