Complex Contagion in Viral Marketing: Causal Evidence and Embeddedness Effects from a Country-Scale Field Experiment

Research on complex contagions suggests that individuals need social reinforcement from multiple sources before they are convinced to adopt costly behaviors. We tested the causal foundation of complex contagions in a country-scale viral marketing field experiment. The experiment used a peer encouragement design in which a randomly sampled set of customers were encouraged to share a coupon for a mobile data product with their friends. This experimental design allowed us to test the causal effects of neighboring adopters on the product adoption of their own neighbors. We find causal evidence of complex contagions in viral marketing: contact with one neighboring adopter increases product adoption 3.5-fold, while contact with a second neighbor increases it 4-fold. We also find that social reinforcement crucially depends on the local network structure that supports or constrains peer influences: the more friends two individuals have in common—the more embedded their relationship is—the stronger the effect. While the effect of social reinforcement is quite large, we show that the ability to generate such reinforcement in a realistic setting may be limited when the marketer cannot directly control the messages that customers send to their friends.