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Happiness spreads socially, study finds

Dec. 4, 2008
Courtesy Harvard Medical School
and World Science staff

If you’re hap­py and you know it, you can thank your friends—and their friends. And their friends, too.

On the oth­er hand, blam­ing oth­ers when you’re sad might be less jus­ti­fi­a­ble.

Happiness is con­ta­gious, re­search­ers have found. In a study that as­sessed nearly 5,000 peo­ple’s hap­pi­ness over two dec­ades, the sci­en­tists found that when some­one be­comes hap­py, that has ef­fects up to three rela­t­ion­ships, or de­grees, re­moved from them. (Im­age cour­tesy KCATA)


That’s the mes­sage from a group of re­search­ers who claim “hap­pi­ness” is­n’t the mere re­sult of a sol­i­tary jour­ney filled with per­son­ally tai­lored self-help tech­niques: ra­ther, joy, like laugh­ter, is con­ta­gious.

In a study that as­sessed nearly 5,000 peo­ple’s hap­pi­ness over two dec­ades, the sci­en­tists found that when some­one be­comes hap­py, that has ef­fects up to three rela­t­ion­ships, or de­grees, away. That is, your hap­pi­ness trig­gers a chain re­ac­tion that ben­e­fits not only your friends, but your friends’ friends, and friends’ friends’ friends.

“Y­our emo­tion­al state may de­pend on the emo­tion­al ex­pe­ri­ences of peo­ple you don’t even know,” said Har­vard Med­i­cal School pro­fes­sor Nich­o­las Chris­takis, who, with James Fowl­er from the Uni­ver­s­ity of Cal­i­for­nia, San Die­go co-authored the stu­dy. “And the ef­fect is­n’t just fleet­ing.” 

The find­ings are pub­lished on­line Dec. 4 in the Brit­ish Med­i­cal Jour­nal.

The hap­pi­ness ef­fect, the re­search­ers added, lasts for up to a year. The re­verse, though, is less true: sad­ness does­n’t spread through so­cial net­works as ro­bustly as hap­pi­ness.

Chris­takis and Fowl­er have been min­ing da­ta from the Fram­ing­ham Heart Study, an on­go­ing, mul­ti­-decade car­di­o­vas­cu­lar study that has gen­er­at­ed reams of da­ta on par­ti­ci­pants’ health and rela­t­ion­ships. The an­a­lysts at­tempted to re­con­struct the so­cial fab­ric in which in­di­vid­u­als were en­meshed and as­sess the rela­t­ion­ship be­tween so­cial net­works and health.

The re­search­ers un­earthed what they called a treas­ure trove of da­ta from ar­chives dat­ing back to 1971. All family changes for each study par­ti­ci­pant, such as birth, mar­riage, death, and di­vorce, were recorded. Par­ti­ci­pants had al­so list­ed con­tact in­forma­t­ion for their clos­est friends, cowork­ers and neigh­bors. Co­in­ci­den­t, many of these friends were al­so study par­ti­ci­pants. 

Fo­cus­ing on 4,739 in­di­vid­u­als, Chris­takis and Fowl­er ob­served over 50,000 so­cial and family ties and an­a­lyzed the spread of hap­pi­ness through­out this group. Us­ing the Cen­ter for Ep­i­de­mi­og­i­cal Stud­ies De­pres­sion In­dex, a ques­tion­naire com­plet­ed by par­ti­ci­pants and de­signed to meas­ure sat­is­fac­tion in life, the re­search­ers found that when some­one be­comes hap­py, a friend liv­ing with­in a mile en­joys a 25 per­cent high­er chance of be­com­ing hap­py. A co-resident spouse ex­pe­ri­ences an 8 per­cent high­er chance; sib­lings liv­ing with­in one mile, 14 per­cent higher; next door neigh­bors, 34 per­cent.

Moreo­ver, a friend of a friend en­joyed a nearly 10 per­cent in­creased chance of be­com­ing hap­py; and that per­son’s own friend, a 5.6 per­cent in­creased chance.

“While all peo­ple are roughly six de­grees sep­a­rat­ed from each oth­er, our abil­ity to in­flu­ence oth­ers ap­pears to stretch to only three de­grees,” said Chris­takis. The “e­mo­tion­al con­ta­gion” al­so seems to be stronger for friends or rel­a­tives who live clos­er, the re­search­ers added.

They al­so found that, con­tra­ry to what your par­ents may have said, pop­u­lar­ity does lead to hap­pi­ness. Peo­ple in the cen­ter of their net­work clus­ters are the most likely peo­ple to be­come hap­py, odds that in­crease to the ex­tent that the peo­ple sur­round­ing them al­so have many friends. How­ev­er, be­com­ing hap­py does­n’t help mi­grate a per­son from the net­work fringe to the cen­ter. Joy spreads through the net­work, the re­search­ers ex­plained, with­out chang­ing its struc­ture.

As for mon­ey—it can buy you just a lit­tle hap­pi­ness, Fowl­er said. The Fram­ing­ham da­ta sug­gested hav­ing $5,000 ex­tra in­creased a per­son’s chances of be­com­ing hap­pi­er by about 2 per­cent, he not­ed. But “the friend of a friend of a friend can have a great­er in­flu­ence than hun­dreds of bills in your pock­et.”


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If you’re happy and you know it, you can thank your friends—and their friends. And their friends, too. On the other hand, blaming others when you’re sad might be less justifiable. That’s the message from a group of researchers who claim “happiness” isn’t the mere result of a solitary journey filled with personally tailored self-help techniques: it’s also a collective phenomenon that spreads through social networks like an emotional contagion. In a study that assessed nearly 5,000 people’s happiness over two decades, the scientists found that when someone becomes happy, that has effects up to three relationships, or degrees, removed from them. That is, your happiness triggers a chain reaction that benefits not only your friends, but your friends’ friends, and friends’ friends’ friends. “Your emotional state may depend on the emotional experiences of people you don’t even know,” said Harvard Medical School professor Nicholas Christakis, who, with James Fowler from the University of California, San Diego co-authored the study. “And the effect isn’t just fleeting.” The findings are to be published online Dec. 4 in the British Medical Journal. The happiness effect, the researchers added, lasts for up to a year. The reverse, though, is less true: sadness doesn’t spread through social networks as robustly as happiness. Christakis and Fowler have been mining data from the Framingham Heart Study, an ongoing, multi-decade cardiovascular study that has generated reams of data on participants’ health and relationships. The analysts attempted to reconstruct the social fabric in which individuals were enmeshed and assess the relationship between social networks and health. The researchers unearthed what they called a treasure trove of data from archives dating back to 1971. All family changes for each study participant, such as birth, marriage, death, and divorce, were recorded. Participants had also listed contact information for their closest friends, coworkers and neighbors. Coincidentally, many of these friends were also study participants. Focusing on 4,739 individuals, Christakis and Fowler observed over 50,000 social and family ties and analyzed the spread of happiness throughout this group. Using the Center for Epidemiological Studies Depression Index, a questionnaire completed by participants and designed to measure of satisfaction in life, the researchers found that when someone becomes happy, a friend living within a mile enjoys a 25 percent higher chance of becoming happy. A co-resident spouse experiences an 8 percent higher chance; siblings living within one mile a 14 percent higher; next door neighbors, 34 percent. Moreover, a friend of a friend enjoyed a nearly 10 percent increased chance of becoming happy; and that person’s own friend, a 5.6 percent increased chance. “While all people are roughly six degrees separated from each other, our ability to influence others appears to stretch to only three degrees,” said Christakis. The “emotional contagion” also seems to be stronger for friends or relatives who live closer, the researchers added. They also found that, contrary to what your parents may have said, popularity does lead to happiness. People in the center of their network clusters are the most likely people to become happy, odds that increase to the extent that the people surrounding them also have many friends. However, becoming happy doesn’t help migrate a person from the network fringe to the center. Joy spreads through the network, the researchers explained, without changing its structure. As for money—it can buy you just a little happiness, Fowler said. The Framingham data suggested having $5,000 extra increased a person’s chances of becoming happier by about 2 percent, he noted. But “the friend of a friend of a friend can have a greater influence than hundreds of bills in your pocket.”