# Epidemic Model **Entity class:** Mathematical model family **Domain:** Epidemiology / complex systems / diffusion **Maturity:** Developed ## Definition An **epidemic model** represents movement among states—commonly susceptible, exposed, infectious, and removed or recovered—using transition rates, contact structure, and time. Compartment models such as [[wiki/SIR Model|SIR]] and [[wiki/SEIR Model|SEIR]] simplify populations into aggregate states; network and [[wiki/Agent-Based Model|agent-based models]] represent heterogeneous contacts and behaviors. When applied to radicalization or terrorism, state names must be translated cautiously. Exposure to content, ideological commitment, recruitment, material support, and violent action are not interchangeable compartments, and an estimated “reproduction number” is a model parameter rather than proof that ideas are biological pathogens. ## Relationships - **canonical forms:** [[wiki/SIR Model|SIR Model]] and [[wiki/SEIR Model|SEIR Model]]. - **network extension:** [[wiki/Network Epidemiology|Network Epidemiology]]. - **event alternative:** [[wiki/Hawkes Process|Hawkes Process]]. - **counterterrorism application:** [[wiki/Epidemiological and Threat Network Analysis|Epidemiological and Threat Network Analysis]]. ## Sources / Provenance - [National Library of Medicine — Epidemiological modeling of terrorist networks](https://pmc.ncbi.nlm.nih.gov/articles/PMC7299159/) - [World Health Organization — Contact tracing](https://www.who.int/news-room/questions-and-answers/item/contact-tracing)