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The basic SIR model is written as a system of ordinary differential equations describing transfers between compartments: susceptibles decrease by infection, infecteds gain infections and lose cases by recovery or removal, and recovereds increase by removal from the infected class. The equations are $\frac{dS}{dt}=-\beta SI$, $\frac{dI}{dt}=\beta SI-\gamma I$, and $\frac{dR}{dt}=\gamma I$.

Conditions: The population is modeled as well mixed.; The dynamics are represented by global rate equations rather than spatially resolved equations.

The basic SIR model is written as a system of ordinary differential equations describing transfers between compartments: susceptibles decrease by infection, infecteds gain infections and lose cases by recovery or removal, and recovereds increase by removal from the infected class. The equations are $\frac{dS}{dt}=-\beta SI$, $\frac{dI}{dt}=\beta SI-\gamma I$, and $\frac{dR}{dt}=\gamma I$.

Conditions: The population is modeled as well mixed.; The dynamics are represented by global rate equations rather than spatially resolved equations.

In the displayed SIR equations, $\beta$ represents the transmission rate per pair of people, one infected and one susceptible, which governs the flow of new infections. $\gamma$ represents the removal or recovery rate, which governs the flow of infected individuals leaving the infected compartment to join the recovered or removed compartment.

Conditions: $\beta$ is the transmission rate per pair.; $\gamma$ is the removal/recovery rate.; The displayed model treats the population as divided into S, I, and R compartments.

In the displayed SIR equations, $\beta$ represents the transmission rate per pair of people, one infected and one susceptible, which governs the flow of new infections. $\gamma$ represents the removal or recovery rate, which governs the flow of infected individuals leaving the infected compartment to join the recovered or removed compartment.

Conditions: $\beta$ is the transmission rate per pair.; $\gamma$ is the removal/recovery rate.; The displayed model treats the population as divided into S, I, and R compartments.