The contagious nature of disease has long been known as illness spreads throughout a social network, but new research suggests that this isn’t the only thing that’s contagious.

Data in the research, in the July 7 Proceedings of the Royal Society, comes from the Framingham Heart Study, a one-of-a-kind project which since 1948 has regularly collected social and medical information from thousands of people in Framingham, Massachusetts.

The research finds that the chances of you being happy increases by 0.02% for each happy person you know, whilst your chances of being sad increase by 0.04% for each unhappy person you know.

Is it statistically significant? How happy are your friends?