The same team that demonstrated obesity¹ and smoking spread in networks has shown that the more happy people you know, the more likely you are yourself to be happy.

And getting connected to happy people improves a person's own happiness, they reported in the British Medical Journal.

"What we are dealing² with is an emotional stampede," Nicholas Christakis, a professor of medical sociology at Harvard Medical School in Boston, said in a telephone interview.

Christakis and James Fowler, a political scientist at the University of California, San Diego, have been using data from 4,700 children of volunteers in the Framingham Heart Study, a giant health study begun in Framingham, Massachusetts in 1948.

They have been analyzing³ a trove⁴ of facts from tracking sheets dating back to 1971, following births, marriages, death, and divorces. Volunteers also listed contact information for their closest friends, co-workers, and neighbors.

They assessed happiness using a simple, four-question test.

"People are asked how often during the past week, one, I enjoyed life, two, I was happy, three, I felt hopeful about the future, and four, I felt that I was just as good as other people," Fowler said.

The 60 percent of people who scored highly on all four questions were rated as happy, while the rest were designated unhappy.

People with the most social connections -- friends, spouses⁶, neighbors, relatives -- were also the happiest, the data showed. "Each additional happy person makes you happier," Christakis said.

And happiness is more contagious⁷ than unhappiness, they discovered.

"If a social contact is happy, it increases the likelihood that you are happy by 15 percent," Fowler said. "A friend of a spouse⁵ or a sibling⁸, if they are happy, increases your chances by 10 percent," he added.

A happy third-degree friend -- a friend of a friend -- increases a person's chances of being happy by 6 percent.

"But every extra unhappy friend increases the likelihood that you'll be unhappy by 7 percent," Fowler said.

该研究小组发现，你周围的人越快乐，你也会越快乐。此前该研究小组发现肥胖和吸烟会传染。

研究人员在《英国医学期刊》上发表的研究报告中称，与快乐的人在一起，你自己也会更快乐。

位于波士顿的哈佛医学院的医药社会学教授尼古拉斯•克里斯塔克斯在接受一个电话采访时说：“这是一个情绪感染的问题。”

克里斯塔克斯教授和加州大学圣地亚哥分校的政治科学家詹姆斯•福勒对参与“弗明汉心脏研究”的4700名儿童志愿者的数据进行了分析。“弗明翰心脏研究”规模宏大，创始于1948年马萨诸塞州的弗明翰市。

研究人员对1971年至今的跟踪调查资料进行了分析，其中包括研究对象的出生、婚姻、死亡和离异等信息。研究对象还列出了他们最亲密的朋友、同事及邻居的联系信息。

研究人员通过一个简单的“四问测试”来评估研究对象的快乐程度。

福勒说：“我们的问题是，在过去一周内，以下四种情绪出现的频率？1享受生活 2 我很快乐；3 对未来充满希望 4 感觉和别人一样好。”

其中有60%的研究对象对所有四个问题的打分都很高，这些人被评定为“快乐”，其他人则被评定为不快乐。

调查数据显示，社会关系最广泛的人同时也最快乐，这些人与朋友、配偶、邻居和亲戚的联系都较为密切。克里斯塔克斯说：“你身边多一个快乐的人，你就多一份快乐。”

研究人员还发现，快乐比不快乐更易“传染”。

福勒说：“如果你的直接社交对象很快乐，你快乐的几率会增加15%。如果你配偶或兄弟姐妹的朋友很快乐，你快乐的几率会增加10%。”

如果你的第三层社交圈，如朋友的朋友很快乐，那么你快乐的几率会增加6%。

福勒说：“但每多一个不快乐的朋友，你不快乐的几率会增加7%。”