When friends smile, people smile with them. And when they are low, people tend to feel sorry for themselves too. A team led by Dr Nicholas Christakis, a sociologist at Harvard Medical School, and including Professor Fowler, made their conclusions after analysing 53,228 social connections between 5,124 individuals over time, reports New Scientist.
The study also discovered that the effect is not down to happy people simply being attracted towards like-minded sorts. Instead, cheerfulness itself is contagious. Dr Christakis said: "If you drop one pebble in a pond, it will create ripples out from the pebble." He added: "Most people will not be surprised that people with more friends are happier, but what really matters is whether those friends are happy."
The researchers found a happy friend increased the odds of someone being happy by 15 per cent -but that a friend of a friend boosted the chance by about 10 per cent, and a friend of a friend of a friend by about six per cent. The study claimed that despite physical proximity, the mood of a cohabiting partner was less than 10 per cent likely to have an effect.
Behaviour including drinking, smoking and even obesity can spread in a similar manner, the team claims. However, a person's chances of becoming obese trebled if they had obese friends, Christakis said. According to the researchers, a whole range of phenomena are 'transmitted' through networks of friends, including happiness and depression, obesity, drinking and smoking habits and even ill-health.
A person's likelihood of voting can also be affected by their friends, as can a taste for certain music or food, a preference for online privacy, and even the tendency to attempt or think about suicide.