S V Subramanian1, Rockli Kim2, Nicholas A Christakis3. 1. Department of Social and Behavioral Sciences, Harvard T.H. Chan School of Public Health, Boston, MA, USA; Harvard Center for Population & Department Studies, Cambridge, MA, USA. Electronic address: svsubram@hsph.harvard.edu. 2. Department of Social and Behavioral Sciences, Harvard T.H. Chan School of Public Health, Boston, MA, USA. 3. Department of Sociology, Yale University, New Haven, CT, USA; Department of Medicine, Yale University, New Haven, CT, USA; Yale Institute for Network Science, Yale University, New Haven, CT, USA.