icm: Stochastic Individual Contact Models

In EpiModel: Mathematical Modeling of Infectious Disease Dynamics

Stochastic Individual Contact Models

Description

Simulates stochastic individual contact epidemic models for infectious disease.

Usage

icm(param, init, control)

Arguments

param	Model parameters, as an object of class param.icm().
init	Initial conditions, as an object of class init.icm().
control	Control settings, as an object of class control.icm().

Details

Individual contact models are intended to be the stochastic microsimulation analogs to deterministic compartmental models. ICMs simulate disease spread on individual agents in discrete time as a function of processes with stochastic variation. The stochasticity is inherent in all transition processes: infection, recovery, and demographics.

The icm function supports the built-in SI, SIR, and SIS disease types only, in one-group or two-group configurations, with or without demography. For custom or extension epidemic models, use the network model class via netsim() with control.net(type = NULL, ...) and user-supplied module functions.

Value

A list of class icm with the following elements:

• param: the epidemic parameters passed into the model through param, with additional parameters added as necessary.

• control: the control settings passed into the model through control, with additional controls added as necessary.

• epi: a list of data frames, one for each epidemiological output from the model. Outputs always include the size of each compartment, as well as flows in, out of, and between compartments.

See Also

Extract the model results with as.data.frame.icm(). Summarize the time-specific model results with summary.icm(). Plot the model results with plot.icm(). Plot a compartment flow diagram with comp_plot().

Examples

## Not run: 
## Example 1: SI Model
param <- param.icm(inf.prob = 0.2, act.rate = 0.25)
init <- init.icm(s.num = 500, i.num = 1)
control <- control.icm(type = "SI", nsteps = 500, nsims = 10)
mod1 <- icm(param, init, control)
mod1
plot(mod1)

## Example 2: SIR Model
param <- param.icm(inf.prob = 0.2, act.rate = 0.25, rec.rate = 1/50)
init <- init.icm(s.num = 500, i.num = 1, r.num = 0)
control <- control.icm(type = "SIR", nsteps = 500, nsims = 10)
mod2 <- icm(param, init, control)
mod2
plot(mod2)

## Example 3: SIS Model
param <- param.icm(inf.prob = 0.2, act.rate = 0.25, rec.rate = 1/50)
init <- init.icm(s.num = 500, i.num = 1)
control <- control.icm(type = "SIS", nsteps = 500, nsims = 10)
mod3 <- icm(param, init, control)
mod3
plot(mod3)

## Example 4: SI Model with Vital Dynamics (Two-Group)
param <- param.icm(inf.prob = 0.4,  inf.prob.g2 = 0.1,
                   act.rate = 0.25, balance = "g1",
                   a.rate = 1/100, a.rate.g2 = NA,
                   ds.rate = 1/100, ds.rate.g2 = 1/100,
                   di.rate = 1/50, di.rate.g2 = 1/50)
init <- init.icm(s.num = 500, i.num = 1,
                 s.num.g2 = 500, i.num.g2 = 0)
control <- control.icm(type = "SI", nsteps = 500, nsims = 10)
mod4 <- icm(param, init, control)
mod4
plot(mod4)

## End(Not run)

EpiModel documentation built on Oct. 16, 2026, 5:07 p.m.