You have recently been the victim of a vicious rumor. No matter how hard you try to dispel the rumor it seems to have a life of its own.

People hear the rumor and then pass it along to others. When you encounter someone who has heard the rumor you convince them it is not true. Then they, in turn, tell a few people the truth before they forget about it.

What are the two stocks in this system? the flows?

Draw a stock and flow diagram depicting the system.

Run the model for 7 days with the following values:

Each person that knows the rumor tells two other people each day
You learn of the rumor at the beginning of the second day
Beginning of the second day you tell the truth to 5 people each day
Each person who has heard the truth tells two others each day
Ten percent of the people who has heard the truth quit telling others each day
Note: The initial number people who know the rumor will be one--the person who starts the rumor!

Now simulate the system for 8 days. Check for reasonableness. What happens to the number of people who believe the rumor on the eighth day? Can a stock of people be negative in a real system?
Why does it become negative? Compare the number leaving the stock with the number in the stock plus the number entering. In a real system can more leave a stock than the sum of those entering and those already there?

Change the model to place a limit on the number leaving the stock so the the level of the stock can not be less than zero. IF the number leaving the stock is more than the number in the stock, take out the number in the stock. OTHERWISE, the number leaving the stock should be as it was before.

Once you have completed the model, show the instructor your final constrained behavior graph.