http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0012948 http://news.sciencenet.cn/htmlnews/2010/9/237677.shtm Social Network Sensors for Early Detection of Contagious Outbreaks Nicholas A. Christakis 1 , 2 , James H. Fowler 3 , 4 ...