... Much of the most credible evidence about peer effects in humans and primates comes from small experiments in artificial social environments (Asch, 1956;Sherif, 1936;Whiten et al., 2005;Herbst and Mas, 2015). In some cases, field experiments modulating tie formation and group membership (Sacerdote, 2001;Zimmerman, 2003;Lyle, 2007;Carrell et al., 2009;Centola, 2010;Firth et al., 2016), shocks to group or peer behavior (Aplin et al., 2015;Banerjee et al., 2013;Bond et al., 2012;Cai et al., 2015;Eckles et al., 2016;van de Waal et al., 2013), or subsequent exposure to peer behaviors (Aral and Walker, 2011;Bakshy et al., 2012a;Salganik et al., 2006) have been possible, but in many cases these experimental designs are infeasible. Thus, much recent work on peer effects uses observational data from new large-scale measurement of behavior (Aral et al., 2009;Bakshy et al., 2011;Friggeri et al., 2014;Ugander et al., 2012;Allen et al., 2013) or longitudinal surveys (Christakis and Fowler, 2007;Iyengar et al., 2011;Banerjee et al., 2013;Card and Giuliano, 2013;Christakis and Fowler, 2013;Fortin and Yazbeck, 2015). ...