It’s long been said that laughter is contagious, and now, it turns out, so is happiness.
Happiness is not an individual but a collective phenomenon, according to a new study released online Thursday in the British Medical Journal.
The study, which followed almost 5,000 people over 20 years, found that happiness can spread through three degrees of separation within social networks, meaning that the happiness of your friend, your friend’s friend, and even your friend’s friend’s friend can infect you with a good mood.
“Happiness not only spreads from person to person but also from person to person to person,” said political scientist James H. Fowler ’92, a professor at the University of California, San Diego and one of the paper’s authors.
The study suggests that the happiest people are those at the center of a social network, Fowler said, comparing this contagion of emotions to catching a sexually transmitted infection.
“For example, in a network of sexual partners, if you have many partners and your partners have many partners, you are more susceptible to catching an STD.” Similarly, Fowler said the most connected people have a greater likelihood of “catching happiness.”
Happily, the study suggests that sadness is not as easily transferred through social networks.
“Unhappiness spreads, but it doesn’t spread quite as much nor does it spread quite as consistently as happiness,” said Harvard Medical School professor Nicholas A. Christakis, who is a co-author of the paper.
Harvard psychology professor Daniel T. Gilbert, a expert on happiness, called the new paper “stunning” in an e-mailed statement.
“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,” Gilbert said. “It is truly amazing to discover that when you replace the word ‘child’ with ‘best friend’s neighbor’s uncle,’ the sentence is still true.”
But some scholars remain skeptical about whether the new findings are accurate. Another recent study in the BMJ cautions that Christakis and Fowler’s happiness study may be skewed.
“Our study certainly does not refute their happiness paper, but it just suggests some caution that if you don’t take care to control for other factors, that you might be finding contagion where none exists,” said Jason M. Fletcher, a professor of public health at Yale.
Fletcher co-authored a study suggesting that perceived network effects could be erroneous. Using the same statistical methods as the happiness study, his study found that characteristics like acne, headaches, and height are contagious among adolescents, indicating that the methods used in the happiness study can produce spurious results.
“There’s no such thing as a social contagion in height,” Fletcher said.
Fletcher and his co-author, B. Cohen-Cole ’95, an economist at the Federal Reserve Bank of Boston, suggested that the happiness study could be biased because happy people are often friends and that their good moods are not necessarily influenced by each other.
“Friends select people to be their friends based on similar characteristics,” said Fletcher, “and potentially happy people choose to be friends with other happy people.”
He added that friends are often exposed to the same environment, including similar levels of crime, risk, and weather, and that those external variables could influence happiness more than a friend’s mood.
In light of these criticisms, both research groups plan to continue probing into the field of happiness with future studies.
“The whole point of science is that you want to capture a great idea but then retain healthy skepticism,” Fowler said.