# Basic Reproduction Number **Entity class:** Epidemiological metric **Aliases:** R0 **Maturity:** Developed ## Definition The **basic reproduction number (R0)** is the expected number of secondary cases generated by one typical infectious case in a wholly susceptible modeled population under specified assumptions. R0 greater than one implies growth in the model; R0 below one implies decline. Applying it to ideology requires explicitly defined states, transmission mechanisms, and observations and should be treated as a modeling analogy rather than a biological diagnosis. ## Relationships - **used in:** [[wiki/SIR Model|SIR Model]], [[wiki/SEIR Model|SEIR Model]], and [[wiki/SERT Model|SERT Model]]. - **analogy:** [[wiki/Radicalization as Social Contagion|Radicalization as Social Contagion]]. - **event alternative:** [[wiki/Hawkes Process|Hawkes Process]]. ## Sources / Provenance - [[research/A Network-Epidemiological Analysis of Radicalization and Real-Time Counterterrorism Observability|Network-Epidemiological Analysis]]