You may think your attentive spouse, your loving children and your good friends are what make you happy. But something else may be going on: The people they're connected with are making you happy too.
So suggests a new study proposing that happiness is transmitted through social networks, almost like a germ is spread through personal contact. The research was published Thursday in BMJ, a British medical journal.
It's the latest in a growing body of work investigating how our social connections - neighbors, friends, family, co-workers, fellow congregants at church and other associates - affect us. The premise is that we live in a social environment that shapes what we do and how we think and feel.
"We've known for some time that social relationships are the best predictor of human happiness, and this paper shows that the effect is much more powerful than anyone realized," said Daniel Gilbert, author of "Stumbling on Happiness" and a professor of psychology at Harvard University.
Previous research by the authors, James Fowler of the University of California-San Diego, and Dr. Nicholas Christakis at Harvard, has concluded that social networks influence obesity and tobacco use by altering perceptions of acceptable weight and desirable behavior.
Now they've turned their attention to the emotional realm, exploring how social ties influence our moods and our sense of well-being. Their primary finding: People who are surrounded by happy people are more likely to be happy themselves. And it's not only people in our immediate circles who make a difference - it's the people surrounding the people we know.
Imagine several pebbles thrown into a pool of water that send ripples outward, said Fowler, an associate professor of political science. Each pebble represents a happy person and the waves the impact of that person's mood on others. This impact, his study found, extends through several degrees of separation, to the friends of a person's friends.
Some experts question whether the researchers' statistical methodology can support that conclusion. It's difficult to sort out cause and effect in this kind of research and the authors may not have done so with enough rigor, said Charles Manski, a Northwestern University economics professor who studies how inferences can be drawn from social interactions.
He asks, is it that one person's happiness makes another person happy, or could it be that another factor experienced by both people is affecting both?
Say two friends are watching a TV show together, and one laughs after the other does, Manski said. It may look like the first person's chuckle is the cause of the second, but the jokes on the TV show might inspire both reactions.
Christakis said his research factored out such mutual influences. The study asked the subjects - 4,739 participants in the famous Framingham Heart Study in Massachusetts - to complete a survey including four questions relating to happiness three times between 1983 and 2003. They also provided information about social contacts, which allow researchers to map their connections.
The study found that happy people form clusters and the happiest people are those most centrally located in the clusters.
"If you imagine the fabric of humanity as a patchwork quilt, it turns out if you're happy or not depends on if you're in a happy or unhappy patch," Christakis said.
"We postulate that people who are in closer, more frequent contact with each other are more susceptible to catching each other's moods," Fowler said.
The researchers stress that personal factors such as jobs or marriages also affect happiness and that although happiness may fluctuate, people tend to return to a personal happiness "set point" over time. It is this relatively stable emotional condition they examined in the paper, not the fleeting moods people experience day to day.
Richard Suzman, director of the division of behavior and social research at the National Institute on Aging, said the line of research holds "enormous promise in helping us improve interventions aimed at helping people change behaviors and improving public health."
Such interventions may involve targeted programs designed to alter social networks that influence behavior. The institute on aging has provided funding for Fowler and Christakis' work.
An editorial accompanying the report in BMJ called its conclusions "intriguing" but advised caution. Framingham, a relatively small community, may prove unique in ways not yet understood, wrote Peter Sainsbury, director of population health in Sydney South West Area Health Service in Australia.
As for whether unhappiness is also spreadable, Fowler and Christakis plan to look at that topic in upcoming papers on loneliness, depression and social networks.
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