1. Public Policy Modeling Causal Loop Diagrams Friday, April 21, 2017
Hun Myoung Park, Ph.D.
Public Management & Policy Analysis Program Graduate School of International Relations

2. Causal Loop Diagram 1
A CLD or causal map depicts the structure of a system or a set of causal relationships among variables (activities) in a system
Used in system dynamics
But general tool to describe concepts (systems) and communicate with others

3. Causal Loop Diagram 2 CLD consists of
Variables of a system. Interdependent (→V →), dependent (→V), and independent (V→)
Cause-and-effect relationships among variables, “S” for the same direction or “O” for the opposite direction
Feedback loop is a closed circuit of interconnection between variables. “R” for reinforcing feedback or “B” for balancing
Delay

4. Drawing a CLD 1
1. Identify a systemic problem that is chronic and recurring and has a history and/or pattern.
2. Set a boundary and level of simplicity

5. Drawing a CLD 2
3. Identify key variables (activities) that are significant events or phenomena that jointly influence the overall system.
Use nouns or noun phrases
Include “the level of,” “the amount of,” “the number of,” or “the size of,” if possible.
Use a neutral or positive term. Avoid such words as “failure” and “increase.”

6. Drawing a CLD 3
4. Begin with more interesting variable (activity) and work backward (begin with an effect and look for its cause) or move back and forth (both directions).
5. Indicate “cause-and-effect” relationship (direction of relationships) using a link and arrow. A departing point influences the destination (A→B).

7. Drawing a CLD 4

8. Drawing a CLD 5
6. Indicate the type of the relationship between two variables on the link.
+ or S (same direction) means a positive relationship between two variables. When A increases, B will increases; When A decreases, B will decreases.
- or O (opposite direction) indicates a negative relationship. If A increases, B will decrease; when A decreases, B will increase.

9. Drawing a CLD 6
7. Delay means that it takes long time for an cause results in its effect.
Depicted by || or “Delay” on the link
“[M]ake system’s behavior unpredictable and confound our efforts to control that behavior.” (Anderson & Johnson,1997, p.57)

10. Drawing a CLD 7
8. If a link between two variables is not clear, redefine the variables or insert an intermediate variable between the two.
9. Keep revising iteratively; No CLD is ever finished. Begin with a simple CLD and try more challenging one incrementally.
10. Label feedback loop with either “R” for reinforcing or “B” for balancing

11. An Example of CLD 1
“Work backward” begins with the important effect and then seeks subsequent cause-effect chains.
“Begin at the beginning” or work forward
“Go back and forth”

12. An Example of CLD 1 Bank failure as a system problem
First ask, “What caused the bank failure?”
Probably “bank’s solvency” is the cause of “bankruptcy (bank failure).”
What is the relationship between the two variables? When bank’s solvency is low, bank failure is more likely (high). – or O
Then ask, “What caused bank’s solvency?” Probably…

13. An Example of CLD 3

14. An Example of CLD 4

15. Software for CLD Vensim (https://vensim.com/)
iThink (
STELLA (
Powersim (
Anylogic (
You may also try LibreOffice Draw or Microsoft Visio

16. Feedback Loop 1
A feedback loop is a closed circle of interconnection between variables or a series of mutual cause and effect (causal relationships).
The loop is internally initiated by the system and insensitive to environment.
Mutual causation is the simplest feedback loop. A→B→A→B→…

17. Feedback Loop 2
Initial cause and ultimate consequence is NOT distinguishable clearly.
“[E]verything is indeed connected to everything else, so, in principle, it doesn’t matter where you start” (Sherwood, 2002: 128).
“[C]ycling back means that what was originally a cause is now suddenly an effect” (Weick, 1979: 77).

18. Feedback Loop 3

19. Feedback Loop 4
“[A]ny change made anywhere will eventually itself be changed by the consequences it triggers” (Weick, 1979: 77)
Given endless cause-effect chains, such distinction is almost meaningless in most circumstance.
The interdependent relationships in a structure (system) are more important.

20. Reinforcing Feedback Loop 1
A reinforcing or positive feedback loop
A feedback loop with even number of negative signs (-) or O (i.e., 0, 2, 4, …).
Depicted by “R” or “+” in the center of a feedback loop
Self-reinforcing feedback or deviation amplifying feedback.
No regulation or control

21. Reinforcing Feedback Loop 2

22. Reinforcing Feedback Loop 3
“Reinforcing loops can be seen as the engines of growth and collapse” (Anderson & Johnson, 1997: 54).
Destabilize the system and deviate from its equilibrium
Form a vicious circle or virtual circle

23. Balancing Feedback Loop 1
A balancing or negative feedback loop
A feedback loop with odd number of negative sign (-) or O (i.e., 1, 3, 5, …).
Depicted by “B” or “-” in the center
Goal seeking feedback, stabilizing feedback, deviation-counteracting, or self-refraining feedback
Since circulation of feedback loop will produce balance or equilibrium.

24. Balancing Feedback Loop 2

25. Multiple Feedback Loop 1
What if there are multiple feedback loops in a system? Some loops are balancing, while others are reinforcing
If “loops are of unequal importance,” then which feedback loop is dominating in the system?
Such dominating or the most important loop will determine the fate of the system in the end (Weick, 1979: 74).

26. Multiple Feedback Loop 2
“[T]he greater the number of inputs to and/or outputs from an element, the more important that element is” (Weick, 1979: 75).
“[C]lose loop that contains the greatest number of these important elements” (Weick, 1979: 75-76)

27. Multiple Feedback Loop 3
In case of equal importance
Count the number of negative loops
Count the total number of negative relationships (count whenever it appears in a feedback loop)
An odd number indicates a balancing or deviation-counteracting system
An even number indicates deviation-amplifying system (Weick, 1979: 76).

28. Change in a System How to change a system?
Change in a relationship from – (opposite) to + (same direction)
Change in a relationship from – (same) to - (opposite direction)
Add some relationships
Delete relationships
Shock (external input) will be decayed without changing the structure of a system

29. Impact of DDT on Malaria 1

30. Impact of DDT on Malaria 2

31. Impact of DDT on Malaria 3

33. Impact of DDT on Malaria 4

34. Impact of DDT on Malaria 4
Loop 1 (Balancing): DDT Use→Mosquito →Disease
Loop 2 (Reinforcing): DDT Use→DDT in Breast Milk→Disease
Loop 3 (Reinforcing): DDT Use→DDT in Gecko→Cat→Rat→Disease
Loop 4 (Reinforcing): DDT Use→Wasp →Caterpillar→Thatch Roof→Disease

35. Economy and Population 1
Sherwood (2002, pp )

36. Economy and Population 2
Sherwood (2002, pp )

37. Economy and Population 3
Sherwood (2002, pp )

38. Economy and Population 4
Sherwood (2002, pp )

39. Economy and Population 5
Sherwood (2002, pp )

40. Economy and Population 6

41. Economy and Population 7

42. Common Pool Resources

43. Corruption System