Ever wonder whether happy people have something you don't, something that keeps them cheerful, chipper and able to see the good in everything? It turns out they do — they have happy friends.

That's the conclusion of researchers from Harvard and the University of California at San Diego, who report in the British Medical Journal online that happiness spreads among people like a salubrious disease. Dr. Nicholas Christakis and James Fowler studied nearly 5,000 people and their more than 50,000 social ties to family, friends and co-workers, and found that an individual's happiness is chiefly a collective affair, depending in large part on his or her friends' happiness — and the happiness of their friends' friends, and even the friends of their friends' friends.

The merriment of one person, the researchers found, can ripple out and cause happiness in people up to three degrees away. So if you're happy, you increase the chance of joy in your close friend by 25%; a friend of that friend enjoys a 10% increased chance. And that friend's friend has a 5.6% higher chance.

"This is a very serious piece of research. It's pioneering," says Dr. Richard Suzman, director of the division of behavioral and social research at the National Institute on Aging. "We are barely beginning to understand its translational and applied aspects."

The authors analyzed data from the Framingham Heart Study, a historic study of heart disease among nearly 5,000 people begun in 1948. Because it was designed to follow participants and their offspring over several generations, the study's creators recorded detailed information about each person's closest relatives and friends, to better keep tabs on the original participants. That database served as an ideal social laboratory for Christakis and Fowler, who questioned each participant and his or her friends and family about their emotional state three times over 20 years.

The idea of mood transfer is not exactly revolutionary. It makes sense, after all, that your happiness will affect your closest friends, and that their emotional state will influence your own. (Interestingly, the same association was not found with unhappiness, despite the old adage about misery and company, and the contagion effect was weaker among family members than friends, possibly because while people take a cue from friends, they take for granted their families and spouses.) What was less expected was that the effect was sustained up to three degrees of separation away, among people who may not necessarily know one another. You may owe your good cheer to your friend's brother's girlfriend, even if you don't know her name.

That's the power of the social network, which, the authors argue, may impact our emotional state even more than our individual choices and environments. And it is not merely a result of like seeking like. The authors compared their observed network with a control network in which they randomly assigned feelings of happiness to individuals, and were able to rule out the possibility that happy people were simply clustering together by choice. Indeed, in another study in the same issue of the BMJ, researchers from Yale University and the Federal Reserve of Boston showed a similar tendency to cluster among people who, for example, are the same height, or suffer from acne, or headaches. But once the researchers adjusted for confounding factors, the network dissolved; in Christakis and Fowler's paper, the happiness link remained unbroken.

But the effect was limited by space and time. Researchers found that the risk of catching happiness increased with proximity: so a next-door neighbor enjoys a 34% increased chance of happiness by living near a happy person, but a friend who lives across town is less affected. And the best-connected social networkers — those who were at the center of their social nodes — were more likely to become happy than people on the fringes. Viral happiness was relatively short lived, however, lasting about a year.

This is the authors' third such networking study suggesting that the social group is a powerful super-organism that wields much influence over individuals' well-being. Previous analyses by Christakis and Fowler, based on the same pool of data, have shown that obesity is similarly contagious, as is the act of quitting smoking.

The researchers' hope is that a better understanding of how people pick up and pass on behaviors will help health officials create more targeted public-health messages. Antismoking campaigns aimed at teens, for example, might be more powerful if they were geared toward the most socially connected students in a high school — rather than individual smokers. "We are always looking for areas to invest in, promising new areas of research that will give us new levels of ability to help people, and without a doubt I see this as a very promising area," says Suzman.

总是在想那些快乐的人们是否拥有一些你所没有的东西，可以让他们保持快乐，爽朗，对于任何事物都能看到其好的一面？事实确实是那样——他们拥有着快乐的朋友们。

这是来自哈佛和圣地亚哥的加利福尼亚大学研究者的结论，他们在英国医学杂志在线版上报告称，快乐像一种有益健康的疾病，在人与人之间传播开来。Nicholas Christakis 和 James Fowler博士研究了近5000人以及超过50000例他们与家人、朋友和同事间的社会关系，然后发现个人的快乐大多是一宗群体事件，大部分依赖于他们的朋友、朋友的朋友、甚至是朋友的朋友的朋友的快乐。研究者发现，一个人的快乐，会产生连锁反应，给三方人群带来快乐。因此，如果你快乐，你亲密朋友快乐的机会会提高25%，他的朋友快乐的机会提高10%，而朋友的朋友的朋友快乐的机会提高5.6%。

“这是一项非常重要的研究，具有开创性意义。”美国国家老年医学研究中心行为与社会研究部门负责人Richard Suzman博士说，“我们才刚刚开始了解它的转化和应用方面。”

作者分析了来自弗雷明汉心脏研究的数据，这是一项关于心脏病方面的历史性研究，开始于1948年，调查了近5000人。因为它旨在对参与者及其后的几代后人进行跟踪研究，该研究发起者详细记录下了参与者最亲密的亲属及朋友的信息，以完善原始参与者的档案。这个数据库成了Christakis 和 Fowler 理想的社会实验室，在20年间，他们对每个参与者及其家人朋友的情绪状态进行了三次调查。

关于情绪感染的说法并不是革命性的，它很容易说得通，毕竟你的快乐会影响你最亲密的朋友，同样，他们的情绪状态也会影响你。（有趣的是，悲伤却不存在这样的关系，尽管有古话说同病相怜，但是悲伤情绪的传播在朋友之间要比在家庭成员之间来的小，可能是因为需要从朋友那获得安慰时，理所当然会先想到家人和配偶。）令人意外的是，这种效应会持续到第三方人群，他们不必认识彼此。就像你可能会从你的朋友的兄弟的女朋友那获得快乐，即使你不知道她的名字。

作者认为，这是由于社会网络的力量，甚至会比我们的选择和环境因素更多地影响我们的情绪状态。这不是一个想当然的结论。作者设置了一个自然观察组和一个对照控制组，在控制组中，他们把研究对象依据快乐情绪进行了随机分配，从而排除了快乐人群因偶然性而聚集在一起的可能性。事实上，在另外一项由英国医学杂志针对同一问题所作的研究中，来自于美国耶鲁大学和波士顿美联储的研究人员，显示了人们在聚集时有一个同样的趋势，比如说，拥有同样的身高，或者同样患有痤疮，或者同样有头痛病。但是，当研究人员调整了研究的混杂因素时，这种网络作用就消失了；而在Christakis 和 Fowler的论文中表明，快乐的联结不会断。

但是这种影响受到空间和空间的限制。研究人员发现，获取快乐的机会随着距离的接近而增加。因此，住在一个快乐的人附近的邻居获得快乐的机会可以增加34%，而住在城市另一端的朋友受到的影响较小。那些联系最紧密的社会关系人（处在他们社会关系网的中心的人们）会比那些处在社会关系网边缘的人更容易获得快乐。然而传染的快乐持续的相对较短，大约一年时间。

作者对于社会网络的第三项研究表明，社会群体是一个强大的超级有机体，相比个人快乐，它发挥了更大影响力。基于相同的调查数据，Christakis 和 Fowler 此前的分析表明，肥胖同样会传染，如同戒烟行为一样。

研究人员们希望，通过对人们怎样习得和传递行为建立一种更好的理解，可以帮助卫生官员采取更多有针对性的公共卫生措施。例如，针对青少年的反吸烟运动，针对处在紧密社会关系中的高中生会比针对个别吸烟者可能会更有效。“我们一直在寻找新的投资领域，希望新的研究领域能够赋予我们新的能力去帮助他人，毫无疑问，我认为这是一个非常有前景的领域。”