From the Washinton Post:

Friday, December 5, 2008

Happiness Can Spread Among People Like a Contagion, Study Indicates

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.

The findings, Christakis and others said, provide striking new
evidence of the power of social networks, which could have
implications for public policy. Happy people tend to be better off in
myriad ways, being more creative, productive and healthier.

"For a long time, we measured the health of a country by looking at
its gross domestic product," said Fowler, a political scientist at the
University of California at San Diego who co-authored the study. "But
our work shows that whether a friend's friend is happy has more
influence than a $5,000 raise. So at a time when we're facing such
economic difficulties, the message could be, 'Hang in there. You still
have your friends and family, and these are the people to rely on to
be happy.' "

Other experts praised the study as a landmark in the growing body of
evidence documenting the influence of personal connections and the
importance of positive emotions.

"It's a pathfinding article," said Martin E.P. Seligman, a University
of Pennsylvania psychologist. "It's totally original, and the findings
are striking."

Stanley Wasserman, who studies social networks at Indiana University,
said: "We've known that one's network ties are important, but we've
never looked at anything on this scale. The implications are you can't
look at individuals as little entities devoid of their social
context."

Others, however, questioned the findings, noting that it is difficult
to account for every variable that might affect the outcomes of such
studies.

"Researchers should be cautious in attributing correlations in health
outcomes of close friends in social network effects," wrote Ethan
Cohen-Cole of the Federal Reserve Bank of Boston and Jason M. Fletcher
of Yale University in an accompanying study. Their research used data
from a large federal survey to show that acne, headaches and even
height could appear to spread through social networks if not analyzed
properly. "The methods of detecting 'social network effects' of health
outcomes commonly found in the recent medical literature might produce
effects where none exists."

But Christakis said his analysis took other possible explanations into
consideration.

Ed Diener, a psychologist at the University of Illinois at
Urbana-Champaign, said the findings could explain why people in some
countries tend to be happier than others. "This is an extremely
exciting study -- interesting, provocative and important," Diener
said.

While obesity appeared to spread even among people who lived far
apart, happiness appears to be transmitted only among people who live
within a mile of one another. The influence was also greatest among
people who considered themselves mutual friends.

Because the researchers did not find the effect for people living on
the same block beyond a next-door neighbor, they were confident that
the positive mood was not the result of living in the same good
neighborhood. Because people tended to get happier if someone they
knew became happy, the researchers could rule out the alternative
explanation that happy people tend to be drawn to each other.

"We know it's not a 'birds of a feather flock together' effect,"
Christakis said.

Surprisingly, happiness had no such effect at work. The researchers
speculated that work relationships may have different dynamics. One
worker might become happy because he or she got a raise or a promotion
at the expense of another, for example.

Unhappiness also appeared to be catching, but not as strongly: An
unhappy connection increased the chances of being unhappy by about 7
percent on average, while a happy connection increased the chances of
being happy by about 9 percent. While having more friends is important
for a person's happiness, the benefit of having more friends appears
to be canceled out if they are unhappy, the researchers found.

The researchers and others speculated that the emotion may be
important on an evolutionary level by helping people cooperate.
Seligman likened happiness to an orchestra tuning up.

"Laughter and singing and smiling tune the group emotionally,"
Seligman said. "They get them on the same wavelength so they can work
together more effectively as group."