Happiness Is Socially Contageous

The Department of Mathematics and Statistics at the University of Vermont finds that your level of happiness is linked to the mood of those you network with on Twitter –  up to three links away from those you directly interact with. The study published in the Journal of Computational Science, and reported in the Huffington Post is titled “Twitter Reciprocal Reply Networks Exhibit Assortativity With Respect to Happiness.” Try tweeting that! The researchers analyzed 40 million messages posted to Twitter over six months and found:

  • Positive mood seems to spread through a network, and so does depression and emotional problems.
  • The more connected users tend to be happier.

Assortativity  is their way of saying that happiness is not random, but that upbeat people manage to find and link with each other. The study focused on connection not just in the sense of following others, but in the sense of a mutual connection in which people have replied to one other.

Methodology: This study used a ‘hedonometer’ for measuring sentiment in text that scores 10,222 of the most used words in the English language on a happiness scale from one to nine. Examples of happiness scores:

  • ‘Love’ scores 8.42.
  • ‘Special’ scores 7.20.
  • ‘Never’ scores 3.34.
  • ‘Sad’ scores 2.38.
  • ‘Die’ scores 1.74.

The average happiness score of a word is measured by an average of 50 independent evaluations, and the happiness of each user was evaluated by applying this hedonometer to all tweets by the user.

Insights: The study found that contentment levels are more similar among nearest neighbors, and drops off the more others are removed from them in social networks. Those scoring high on happiness, have happier immediate twitter interaction neighbors than those whose happy neighbors are 2 or 3 links away.  The further from a happy neighbor one is, the more happiness declines.

Another finding: Once your network approaches 150, it appears impossible to keep up regular meaningful social contact. (This is known as the “Dunbar number,” named for anthropologist Robin Dunbar who proposed that 150 is “roughly the maximum number of relationships it’s possible to pragmatically maintain.”


150 appears a kind of fundamental limit of our social universe and there are even some theories that our brain cortex size has evolved to cope with this number and no more. Indeed one theory of unhappiness is that our modern world has become too socially complex and as a result we suffer. For example, we no longer live in communities which help us achieve the magic Dunbar number.

“Do you tweet?”

Proviso: Causality isn’t proven. We aren’t sure whether happy people just tend to find each other and, conversely, “misery loves company”, or whether happiness is viral, although previous research is said to support the latter contagion theory:

  • The Framingham Heart Study that observed 4739 people from 1983 to 2003 found happy and unhappy people tend to cluster, and that happiness spreads up to three degrees of separation (to  friends of  friends’ friends.)
  • A study by James Fowler and Nicholas Christakis of Harvard Medical School found that those who are surrounded by happier people and who are central in a social network are more likely to become happy in the future.
  • Other research suggests that obesity, alcohol use and smoking are influenced by social networks.

The Harvard Medical School study by James Fowler and Nicholas Christakis mapped connections and influences among nearly 5,000 individuals with data from the Framingham Heart Study over 20 years. Participants in that study listed contact information for their closest friends, family members and neighbors, connecting the researchers to more than 50,000 social ties. They used the Center for Epidemiological Studies Depression Index — a standard set of questions psychologists use to measure happiness — to analyze the cheeriness of the study participants.

They found that when someone gets happy, that person’s friend experiences a 25% increased chance of becoming happy. A friend of that friend experiences a nearly 10% chance of increased happiness, and a friend of that friend has a 5.6% increased chance of happiness. For instance, A friend who lives within a mile and becomes happy increases the probability that you will be happy by 25%. These effects don’t occur between co-workers, and decay with time and geographical separation. According to the authors, as reported in Chief Happiness Officer:

That means a stranger’s good mood can do more to lift your spirits than a $5,000 raise, which only increased happiness 2 percent.

Fortunately, this study found sadness to be less contagious because, according to the study, sadness makes you pull away from others, giving them less exposure to your bad mood.

Implications: The research is provocative in many ways. For instance:

  • Eating disorders might be spread through social networking.
  • The future may see faster spreading epidemics of psychological dysfunction due to social networking.

 raise the question:

If we should increasingly regard emotions as kinds of infectious diseases, does this mean we should screen more carefully who we mingle with, and even quarantine some?