# Complex Contagion **Entity class:** Network diffusion model **Domain:** Network science / sociology / behavioral diffusion **Maturity:** Developed ## Definition **Complex contagion** describes adoption that usually requires reinforcement from multiple contacts, repeated exposures, or social confirmation. It differs from **simple contagion**, where one contact may be sufficient to transmit an infection or item of information. The concept is especially useful for high-cost, identity-laden, or risky behavior. In radicalization analysis, commitment may depend on trusted peers, group norms, identity fusion, and repeated interaction. Network position, clustering, and strong ties can therefore matter more than raw exposure counts. The model still does not convert association into causation or predict an individual act from contact alone. ## Relationships - **studied with:** [[wiki/Social Network Analysis|Social Network Analysis]] and [[wiki/Graph Analytics|Graph Analytics]]. - **applied to:** [[wiki/Radicalization as Social Contagion|Radicalization as Social Contagion]]. - **contrasts with:** simple-contagion assumptions in some [[wiki/SIR Model|SIR]] and [[wiki/SEIR Model|SEIR]] applications. - **network features:** [[wiki/Homophily|Homophily]], [[wiki/Community Detection|Community Detection]], and [[wiki/Structural Holes|Structural Holes]]. ## Sources / Provenance - Damon Centola and Michael Macy, “Complex Contagions and the Weakness of Long Ties,” *American Journal of Sociology* 113, no. 3 (2007). - [National Institute of Justice — Social networks and domestic radicalization](https://nij.ojp.gov/library/publications/role-social-networks-facilitating-and-preventing-domestic-radicalization-what)