This model is derived from the paper "Nobody Ever Gets Credit for Fixing Problems that Never Happened: Creating and Sustaining Process Improvement" by Nelson P. Repenning and John D Sterman. See Insight 752 for a causal loop version of this model.

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The interaction of a population of Moose and Wolves.

There are about fifteen known archetypes with an interesting set of relationships among them.

There is a new version of this model at

Frequently Recurring Structures

All you wanted to do was put a bird feeder in your yard to attract birds and make for a more pleasant morning. And...

When endeavoring to develop an understanding of the nature of something it is generally useful to create a model of some type to aid in surfacing that understanding.

Consider the following "Sustaining the Forest" model intended to provide another example of how unexpected the behavior of a web of extended interactions can be.

There are limits to what one can infer from a qualitative model.

While these pictures represent very different things there is a common essence.

This Romeo and Juliet Model was adapted by Geoff McDonnell from Michael J Radzicki (1993) Dyadic processes, tempestuous relationships, and system dynamics, System Dynamic Rev. 9 (1) :79-94

What do activities of these images have in common?

This is a more Traditional Career Model of how education works, with an increased lifetime earnings from going to college. The following are links to the other two models in the series.

• Loan Cost Model
• Savings Model

This model is derived from the paper "Nobody Ever Gets Credit for Fixing Problems that Never Happened: Creating and Sustaining Process Improvement" by Nelson P. Repenning and John D Sterman. See Insight 9781 for a simulation of this model.

The following model was submitted by Lise Inman & Keith Margerison for inclusion in the ILE currently under development. I think it's a useful model which gets interesting as the arrival interval gets smaller and the queue backs up. So, what do you think of the model and what insights can we surface with this model?

All you wanted to do was put a bird feeder in your yard to attract birds and make for a more pleasant morning. And...

How a Savings Account works.

The model construction process is actually a balancing loop which endeavors to employ an abstract version of real events to form a model which produces conclusions and behavior which mimic the real events.

Little Red Riding Hood walking through the woods to Grandma's house. How long will it take?

The structure responsible for rabbit population growth.

When one undertakes to create a model there are a number of guidelines that are considered essential for consideration if there is to be a success with the model.

Are there environmental/physical limits to humanity? Based on the Are There Limits? blog post by Tom Fiddaman.

From Jay Forrester 1971 book World Dynamics, the earlier, simpler version of the World 3 Limits to Growth Model. Adapted by Geoff McDonnell from Mark Heffernan's ithink version at Systemswiki.org.

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The purpose of this model is to have the user change the value of stocks, flows and converters to experience a variety of different graphical results. Understanding this generic model is important pre-requisite to learning about intravenous drugs in the body, radioactivity, self-esteem, water flowing from a drain and many other basic natural systems.

CLD of Eric Wolstenholme Syst. Dyn. Rev. 23, 371–389, (2007) See IM-1008 for a stock flow version.

Yesterday's actions are responsible for the world we experience today. And today's actions are responsible for the world that we will experience tomorrow. The "Creating the Future" model is intended to provide a better sense of the common process associated with the unexpected unfolding of the future..