Professor of Social and Natural Science Nicholas Christakis ’84 researches the ways in which networks impact behavior, health, and longevity. In a recent study released this month in the journal PLOS ONE, Christakis, along with researchers from the University of California and Facebook Inc., discovered that emotions spread through the social networking site just like other phenomena such as disease spread through real networks of people. After analyzing over a billion Facebook statuses, the researchers discovered that positive posts, on average, resulted in 1.75 more positive posts from friends, and negative posts generated 1.29 further negative posts. At Yale, Christakis co-directs the Yale Institute for Network Science (YINS), which opened last summer. The News spoke with Christakis on Monday about the network of emotions on Facebook and how studying network interactions can improve public policy.