Happiness can be contagious, according to a study carried out by researchers at Harvard Medical School and the University of California, San Diego. The researchers used data from the Framingham Heart Study, a famous ongoing study into cardiovascular risk with participants in the town of Framingham, Massachusetts. Their study focused on 4,739 participants in the Framingham Heart Study who completed a range of information about their levels of happiness and their social networks. The researchers found that when someone became happy a friend, living within a mile, experienced a 25% increased chance of becoming happy themselves. Their spouse had an 8% increased chance, siblings living within a mile 14% and next-door-neighbours 34%. However, not only did that person's friends become happier, their friends' friends had a 10% chance of increase happiness and their friends' friends' friends had a 5.6% chance of increased happiness. The effects were limited by geographical distance from the original person and time, lasting about a year. People who were at the centre of social networks were happier than those at the fringes. Having a $5,000 boost to one's income, however, was only associated with a 2% increase in happiness. Sadness was not found to 'flow' through networks in the same way that happiness did.
You can find out more about this research by clicking on the link in the title of this post.