This model simulates the spread of a disease through a population. This population can consist of either students, which are turtles controlled by individual students via the HubNet Client, or turtles that are generated and controlled by NetLogo, called androids, or both androids and students.

Turtles move around, possibly catching an infection. Healthy turtles on the same patch as sick turtles have a INFECTION-CHANCE chance of becoming ill. A plot shows the number of sick turtles at each time tick, and if SHOW-ILL? is on, sick turtles have a red circle attached to their shape.

Initially, all turtles are healthy. A number of turtles equal to INITIAL-NUMBER-SICK become ill when the INFECT button is depressed.

For further documentation, see the Participatory Simulations Guide found at http://ccl.northwestern.edu/ps/

HOW TO USE IT

Quickstart Instructions:
Teacher: Follow these directions to run the HubNet activity.
Optional: Zoom In (see Tools in the Menu Bar)
Optional: Change any of the settings. If you want to add androids press the CREATE ANDROIDS button. Press the GO button.
Everyone: Open up a HubNet client on your machine and type your user name, select this activity and press ENTER.
Teacher: Have the students move their turtles around to acquaint themselves with the interface. Press the INFECT button to start the simulation.
Everyone: Watch the plot of the number infected.
Teacher: To run the activity again with the same group, stop the model by pressing the NetLogo GO button, if it is on. Change any of the settings that you would like. Press the CURE-ALL button to keep the androids, or SETUP to clear them
Teacher: Restart the simulation by pressing the NetLogo GO button again. Infect some turtles and continue.
Teacher: To start the simulation over with a new group, stop the model by pressing the GO button, if it is on, have all the students log out or press the RESET button in the Control Center, and start these instructions from the beginning

Buttons:
SETUP - returns the model to the starting state, all student turtles are cured and androids are killed. The plot is advanced to start a new run but it is not cleared.
CURE-ALL - cures all turtles, androids are kept. The plot is advanced to start a new run but it is not cleared.
GO - runs the simulation
CREATE ANDROIDS - adds randomly moving turtles to the simulation
INFECT - infects INITIAL-NUMBER-SICK turtles in the simulation
NEXT >>> - shows the next quick start instruction
<<< PREVIOUS - shows the previous quick start instruction
RESET INSTRUCTIONS - shows the first quick start instruction

Sliders:
NUMBER - determines how many androids are created by the CREATE ANDROIDS button
ANDROID-DELAY - the delay time, in seconds, for android movement - the higher the number, the slower the androids move
INITIAL-NUMBER-SICK - the number of turtles that become infected spontaneously when the INFECT button is pressed
INFECTION-CHANCE - sets the percentage chance that every tenth of a second a healthy turtle will become sick if it is on the same patch as an infected turtle

Switches:
WANDER? - when on, the androids wander randomly. When off, they sit still
SHOW-SICK? - when on, sick turtles add to their original shape a red circle. When off, they can move through the populace unnoticed
SHOW-SICK-ON-CLIENTS? - when on, the clients will be told if their turtle is sick or not.

Monitors:
TURTLES - the number of turtles in the simulation
NUMBER SICK - the number of turtles that are infected

Plots:
NUMBER SICK - shows the number of sick turtles versus time

Client Information
After logging in, the client interface will appear for the students, and if GO is pressed in NetLogo they will be assigned a turtle which will be described in the YOU ARE A: monitor. And their current location will be shown in the LOCATED AT: monitor. If the student doesn't like their assigned shape and/or color they can hit the CHANGE APPEARANCE button at any time to change to another random appearance.

The SICK? monitor will show one of three values: "true" "false" or "N/A". "N/A" will be shown if the NetLogo SHOW-ILL-ON-CLIENTS? switch is off, otherwise "true" will be shown if your turtle is infected, or "false" will be shown if your turtle is not infected.

The student controls the movement of their turtle with the UP, DOWN, LEFT, and RIGHT buttons and the STEP-SIZE slider. Clicking any of the directional buttons will cause their turtle to move in the respective direction a distance of STEP-SIZE.

THINGS TO NOTICE

No matter how you change the various parameters, the same basic plot shape emerges. After using the model once with the students, ask them how they think the plot will change if you alter a parameter. Altering the initial percentage sick and the infection chance will have different effects on the plot.

THINGS TO TRY

Use the model with the entire class to serve as an introduction to the topic. Then have students use the NetLogo model individually, in a computer lab, to explore the effects of the various parameters. Discuss what they find, observe, and can conclude from this model.

EXTENDING THE MODEL

Currently, the turtles remain sick once they're infected. How would the shape of the plot change if turtles eventually healed? If, after healing, they were immune to the disease, or could still spread the disease, how would the dynamics be altered?

CREDITS AND REFERENCES

To refer to this model in academic publications, please use: Wilensky, U. and Stroup, W. (1999). NetLogo HubNet Disease model. http://ccl.northwestern.edu/netlogo/models/HubNetDisease. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.

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NetLogo Models Library:HubNet Activities

Disease

NetLogo Models Library:
HubNet Activities