The power of happiness

Happiness is contagious, spreading among friends, neighbors, siblings and spouses like the flu, according to a large study that for the first time shows how emotion can ripple through clusters of people who may not even know each other.

The study of more than 4,700 people who were followed over 20 years found that people who are happy or become happy boost the chances that someone they know will be happy. The power of happiness, moreover, can span another degree of separation, elevating the mood of that person's husband, wife, brother, sister, friend or next-door neighbor.

"You would think that your emotional state would depend on your own choices and actions and experience," said Nicholas A. Christakis, a medical sociologist at Harvard University who helped conduct the study published online today by BMJ, a British medical journal. "But it also depends on the choices and actions and experiences of other people, including people to whom you are not directly connected. Happiness is contagious."
One person's happiness can affect another's for as much as a year, the researchers found, and while unhappiness can also spread from person to person, the "infectiousness" of that emotion appears to be far weaker.

Previous studies have documented the common experience that one person's emotions can influence another's -- laughter can trigger guffaws in others; seeing someone smile can momentarily lift one's spirits. But the new study is the first to find that happiness can spread across groups for an extended period.

When one person in the network became happy, the chances that a friend, sibling, spouse or next-door neighbor would become happy increased between 8 percent and 34 percent, the researchers found. The effect continued through three degrees of separation, although it dropped progressively from about 15 percent to 10 percent to about 6 percent before disappearing.

The research follows previous work by Christakis and co-author James H. Fowler that found that obesity also appears to spread from person to person, as does the likelihood of quitting smoking. The researchers have been using detailed records originally collected by the Framingham Heart Study, a long-running project that has explored a host of health issues, to construct and analyze detailed maps of social networks.

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