StarLogo Project:

Epidemic

WHAT IS IT?

This project presents a very simple model for the spread of a disease. There are two types of creatures: healthy creatures (green) and sick creatures (red). When a healthy creature comes in contact with a sick creature, it becomes sick.

HOW TO USE IT

Click the setup button to setup the creatures. Click the go button to start the simulation.

The INFECTED-% monitor shows the percentage of sick creatures.

The number slider controls the number of creatures. (Changes in this slider do not take effect until the next setup.) The init-infected slider controls the initial number of sick creatures. The recover slider controls the rate at which sick creatures become healthy.

THINGS TO NOTICE

If you start with just one sick creature, the disease spreads slowly at first. But as more creatures become infected, the disease spreads rapidly. The spread of the disease is a good example of exponential growth.

If the recover slider is set at greater than zero, sick creatures have a chance to become healthy again. So there are two competing forces: disease spreads by contact, but sick creatures have a probabilistic chance to become healthy again. Over time, the overall percentage of sick creatures should reach a rough equilibrium.

EXPLORATIONS

How do changes in the recover rate affect the equilibrium percentage of infected creatures? How is the equilibrium affected by changes in the total number of creatures?

STARLOGO FEATURES

The color coding of the creatures is not just for display purposes. The coloring is also used to calculate the total number of sick creatures, using the count-color primitive.