The same team that demonstrated obesity and smoking spread in networks has shown that the more happy people you know, the more likely you are yourself to be happy.
And getting connected to happy people improves a person's own happiness, they reported in the British Medical Journal.
"What we are dealing with is an emotional stampede," Nicholas Christakis, a professor of medical sociology at Harvard Medical School in Boston, said in a telephone interview.
Christakis and James Fowler, a political scientist at the University of California, San Diego, have been using data from 4,700 children of volunteers in the Framingham Heart Study, a giant health study begun in Framingham, Massachusetts in 1948.
They have been analyzing a trove of facts from tracking sheets dating back to 1971, following births, marriages, death, and divorces. Volunteers also listed contact information for their closest friends, co-workers, and neighbors.
They assessed happiness using a simple, four-question test.
"People are asked how often during the past week, one, I enjoyed life, two, I was happy, three, I felt hopeful about the future, and four, I felt that I was just as good as other people," Fowler said.
The 60 percent of people who scored highly on all four questions were rated as happy, while the rest were designated unhappy.
CONNECTIONS EQUAL HAPPINESS
People with the most social connections -- friends, spouses, neighbors, relatives -- were also the happiest, the data showed. "Each additional happy person makes you happier," Christakis said.
"Imagine that I am connected to you and you are connected to others and others are connected to still others. It is this fabric of humanity, like an American patch quilt."
Each person sits on a different-colored patch. "Imagine that these patches are happy and unhappy patches. Your happiness depends on what is going on in the patch around you," Christakis said.
"It is not just happy people connecting with happy people, which they do. Above and beyond, there is this contagious process going on."And happiness is more contagious than unhappiness, they discovered.
"If a social contact is happy, it increases the likelihood that you are happy by 15 percent," Fowler said. "A friend of a friend, or the friend of a spouse or a sibling, if they are happy, increases your chances by 10 percent," he added.
A happy third-degree friend -- the friend or a friend of a friend -- increases a person's chances of being happy by 6 percent.
"But every extra unhappy friend increases the likelihood that you'll be unhappy by 7 percent," Fowler said.
The finding is interesting but it is useful, too Fowler said.
"Among other benefits, happiness has been shown to have an important effect on reduced mortality, pain reduction, and improved cardiac function. So better understanding of how happiness spreads can help us learn how to promote a healthier society," he said.
The study also fits in with other data that suggested -- in 1984 -- that having $5,000 extra increased a person's chances of becoming happier by about 2 percent.
"A happy friend is worth about $20,000," Christakis said.
His team also is examining the spread of depression, loneliness, and drinking behavior. [via reuters]