1. Feedback Loop Diagrams Different Diagrams for Different Stages of the Modeling Process
Step 1
A is for get Acquainted
Get acquainted with the client, the system & the problem
Step 2
B is for Be specific
Be specific about the dynamic problem
Step 3
C is for Construct
Construct the sock and flow diagram
Step 4
D is for Draw
Draw the causal loop diagram
Step 5
E is for Estimate
Estimate the parameter values
Step 6
R is for Run
Run the model to get the reference mode
Step 7
S is for Sensitivity
Conduct sensitivity analysis
Step 8
T is for Test
Test the impact of policies
These slides focus on the conventions for “word and arrow” diagrams in Step 4; their the purpose is to check if the model has the necessary feedback loops to generate the “Reference Mode.”
A 2nd type of causal loop diagram can be useful in the initial “Brain Storming.” These diagrams can explode in size, perhaps growing to include 50 or more loops. They are not discussed here.
My experiences with clients have led me to leave the word and arrow diagrams at home when talking with clients. The slides conclude with an alternate, much more effective, way to show clients how the key loops are simulated in the model.

2. Population Model Example

3. Home Heating Example

4. Why Draw These Diagrams?
To see the feedback loops
There are two kinds of loops
Positive feedback loop
Negative feedback loop
The diagrams are for thinking and discussion (not for simulation)

5. Positive Feedback Loops
Can often lead to exponential growth
Or they can lead to rapid decline
If the changes are good, then “virtuous circles”
If changes are bad, “vicious circles”
The loop acts to magnify the effect of outside disturbances
0, 2, 4,6 (any even number) of – arrows in the loop

6. Negative Feedback Loops
Can often lead to exponential decline
Or they may serve as control loops
with an explicit goal (i.e., engineered like a thermostat)
or with an implicit goal (a natural system)
The loop acts to negate the effect of outside disturbances
1, 3, 5,7 (any odd number) of – arrows in the loop
Tend to be much more prevalent than positive feedback loops

7. Figs 9.4,5,6. Guidelines for labeling an arrow as + or -

8. Supply & Demand: Example of coupled loops.
Two Negative Feedback Loops: Do these act to “negate” the effect of outside disturbances?

9. Boom Town Housing Problem (my first problem after graduate school)

10. Look for the Feedback and you will see the “Big Picture”
And you will probably by the ONLY person to simulate the key loop!

11. D is for Draw the Causal Loop Diagram
The previous examples start from scratch. The diagrams to illustrate the way we label each arrows and the way we label each loop.
Now, suppose we already have a model and we proceed to step 4: D is for Draw the feedback loops in the model.

12. Population Model Diagram
Start with the stocks, then add the flows

13. Then explain the flows, best to start with the easy flows

14. Next: explain the births

15. When Do We Draw the Causal Loop Diagrams?

16. S-Shaped Growth Examples
Flowers Model
Sales Company Model
Epidemic Model

17. Loops in the Flowers Model

18. Loops in the Sales Model

19. Loops in an Epidemic Model

20. Plug in Symbols for “interpretation”
Positive Feedback Loops (+)
Negative Feedback Loops (-)

22. Advice for Beginners
Avoid “action words.” The “action is in the arrows, not in the words”
Avoid “too many arrows” – your goal is to show the loops, not the clutter.

23. Exercises: Find the Errors

24. How Many Loops?

25. Label the Loops in this Diagram

26. Show the Stock & Flow Diagram instead.
OK, Now you know how to draw causal loop diagrams for sharing within the System Dynamics Community
But how should we show the key feedback loops in the model to the client? especially a client that advises us to Please leave those word and arrow diagrams at home.
Show the Stock & Flow Diagram instead.
and Name the Loops!

27. Naming the 3 loops in the Sales Model

28. Naming the 3 loops in an Epidemic Model

29. Naming the 2 loops in the Model of Office Space Construction

30. Final Example: The Striga Model (thanks to Timothy Silberg, Michigan State University)
Naming the Loops is one of several things we can do for clarity