“…However, recently there has been increasing interest in settings where treatments 'spill over' from the treated individual to his or her social contacts, or where outcomes are contagious. Researchers who are interested in causal inference have developed methods for interferencewhen one individual's treatment or exposure affects not only his own outcome but also the outcomes of his contacts (Aronow and Samii, 2017;Athey et al, 2018;Bowers et al, 2013;Eckles et al, 2016;Forastiere et al, 2020;Graham et al, 2010;Halloran and Hudgens, 2012;Raudenbush, 2006, 2008;Hudgens and Halloran, 2008;Jagadeesan et al, 2020;Liu and Hudgens, 2014;Liu et al, 2016;Ogburn and VanderWeele, 2014;Rosenbaum, 2007;Rubin, 1990;Sobel, 2006;Tchetgen Tchetgen and VanderWeele, 2012;VanderWeele, 2010). Researchers who are interested in social networks have attempted to model the spread of contagious outcomes across network ties (Christakis and Fowler, 2007, 2008, 2010Ali and Dwyer, 2009;Cacioppo et al, 2009;Lazer et al, 2010;Rosenquist et al, 2010), but existing methods for such modelling are either flawed (Cohen-Cole and Fletcher, 2008;Lyons, 2011;Shalizi and Thomas, 2011) or limited by strong assumptions and burdensome data requirements.…”