SIR with Scroll Bars

What does this Model Represent?

This model illustrates the spread of a disease through a population, as susceptible people become infected, then infected people recover.

What are the elements of this Model?

Columns/Lines on the Graph

• Susceptible – Have not caught the disease, vulnerable to catching it by interacting with infected people.
• Infected – Have the disease, capable of passing the disease on, could possibly recover.
• Recovered – No longer have the disease, immune to catching it again, remain immune for the rest of the time.

Slider Bars

• Infection Rate – The chance that a susceptible person has of catching the disease through interacting with an infected person.
• Cure Rate – The chance that an infected person has of recovering from the disease.
• DT – The size of each time step (delta time).

How do I use this Model?

Change the values of the sliders and observe the effect it has on the graph.

What should I expect?

As the Infection Rate is increased, the three lines on the graph should be “squashed” towards the left, as the disease is spreading faster. If it is decreased, the graph will be horizontally “stretched” as the disease takes longer to spread.

As the Cure Rate is increased, the Recovered line has a steeper slope and Infected has a smaller peak, as people become recovered faster. As it is decreased, the Recovered line has a shallower slope, and the peak number of Infected people approaches the number of Susceptible people.

As DT is increased, the graph should keep its basic shape, but the markers on the graph will be spaced further apart. As it is decreased, the markers will be closer together, resulting in a smoother graph.

Download the model file.