1. From the Department of Social and Behavioral Sciences, Harvard School of Public Health, Cambridge, MA (M.A., I.K., S.V.S.); Department of Epidemiology and Biostatistics, University of California–San Francisco School of Medicine (M.M.G.); Federal Reserve Bank of Boston, Boston, MA (P.C.); and Yale Institute for Network Science, Yale University, New Haven, CT (N.A.C.).