# SIR Model **Entity class:** Compartmental epidemic model **Domain:** Mathematical epidemiology / diffusion **Maturity:** Developed ## Definition The **SIR model** partitions a population into **susceptible (S)**, **infectious (I)**, and **recovered or removed (R)** compartments. In its basic form, transitions depend on a transmission parameter, contact between S and I, and a removal or recovery parameter. The ratio of those rates contributes to the basic reproduction number, **R0**. Counterterrorism researchers may borrow the structure to simulate recruitment or ideological diffusion, but the mapping is an abstraction. A person can hold several identities, change behavior without changing belief, relapse, conceal activity, or influence others without occupying a stable “infectious” state. ## Relationships - **member of:** [[wiki/Epidemic Model|Epidemic Model]]. - **adds latent state in:** [[wiki/SEIR Model|SEIR Model]]. - **network refinement:** [[wiki/Complex Contagion|Complex Contagion]] and [[wiki/Network Epidemiology|Network Epidemiology]]. - **application boundary:** [[wiki/Radicalization as Social Contagion|Radicalization as Social Contagion]]. ## Sources / Provenance - [National Library of Medicine — Epidemiological modeling of terrorist networks](https://pmc.ncbi.nlm.nih.gov/articles/PMC7299159/)