In the other words, one person's happiness can spread outward through three degrees of separation. Those at the center of such circles may be people that "you have never met. But their mood can have a profound effect on your own mood," Fowler said.
The researchers tried to adjust their statistics to account for factors that could possibly affect the trends, such as people being more likely to choose friends who are like them.
The findings were published online Dec. 5 in the British Medical Journal.
Fowler said the study has "totally changed the way I see the world."
"To think about the way we're connected to one another has caused me to take more responsibility for my own actions," he said. "If I head home in a happy mood, I'm not just making my son happy, I'm potentially making my son's friend happy. I'm not just making my wife happy, I'm making my wife's mother happy."
Rosemary Blieszner, a professor of human development at Virginia Tech, called the study findings impressive, because they relied on a large sample of participants who were followed for a long period of time.
Overall, the study reveals the importance of the company people keep, Blieszner said.
"People who are surrounded by many happy people are more likely to be happy in the future than those who are surrounded by unhappy people," she said.
To learn more about happiness, check with the Pew Research Center.
SOURCES: James Fowler, Ph.D., associate professor of political science, University of California, San Diego; Rosemary Blieszner, Ph.D., professor of human development, Virginia Polytechnic Institute and State University, Blacksburg, Va.; Dec. 5, 2
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