Social scientists are discovering they can learn a lot by plugging into social media.
A team at Cornell University in Ithaca, N.Y., has been able to chart hourly, daily and seasonal mood changes in the global population by studying Twitter.
Michael Macy and Scott Golder utilized language-monitoring software to scan more than 500 million tweets from 2.4 million users in 84 countries over a two-year period. In particular, the program searched for words with positive connotations (awesome, pretty, fantastic) and negative connotations (afraid, sad, enemy) and then analyzed when they were most commonly used during the day.
The results, published Friday in the journal Science, revealed that people around the planet experience similar rhythms in their moods.
"We found that there is a very robust pattern worldwide in which people's positive mood peaks in the morning around breakfast time and then it goes downhill from there in the course of the day. But it rebounds in the evening," said Dr. Macy, who is a professor of sociology.
"And we find this pattern is repeated on weekends, but the morning peak is delayed about two hours, which suggests that people are waking up later than they do on weekdays."
Dr. Macy speculated that these daily mood swings are partly driven by biological forces including circadian rhythm, the body's 24-hour internal clock. Social factors, such as work and relaxation schedules, likely play a role, too, he added.
The study also found that people, on average, tend to be happier on weekends. What's more, seasonal changes have a discernible influence on how we feel. "When the days are getting longer, people are in a better mood than when the days are getting shorter," Dr. Macy said.
There were some significant exceptions to these general patterns. Night owls – or, in the case of this study, people who are very active on Twitter in the wee hours of the morning – did not exhibit the normal upswing in mood at the end of the day.
In some respects, the overall findings may not seem especially surprising or profound. But Mr. Golder, a graduate student in sociology, noted that researchers have never been able to follow so many people in real time. Their work, in the past, has relied on opinion surveys, laboratory experiments and field observations of small groups of individuals.
"The Internet is bringing powerful new tools to the social sciences," Mr. Golder said. "Twitter has been criticized for being mundane; some say it's just comments from celebrities or people chatting with friends about what they had for lunch and things like that," he said.
"But it can be really interesting. When you start to aggregate the data, you can learn things about populations on a large scale. "