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Public Policy Modeling
Causal Loop Diagrams Wednesday, April 19, 2023
Hun Myoung Park, Ph.D.
Public Management & Policy Analysis ProgramGraduate School of International Relations
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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
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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
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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
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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.”
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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).
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Drawing a CLD 4
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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.
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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)
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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
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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”
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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…
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An Example of CLD 3
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An Example of CLD 4
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Software for CLD
• Vensim (https://vensim.com/)
• iThink (http://www.iseesystems.com/)
• STELLA (http://www.iseesystems.com/)
• Powersim (http://www.powersim.com/)
• Anylogic (http://www.anylogic.com/)
• You may also try LibreOffice Draw or Microsoft Visio
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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→…
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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).
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Feedback Loop 3
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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.
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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
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Reinforcing Feedback Loop 2
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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
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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.
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Balancing Feedback Loop 2
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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).
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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)
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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).
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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
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Impact of DDT on Malaria 1
DDT UseDisease (Malaria)
Mosquito
S
O
S
B1
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Impact of DDT on Malaria 2
DDT UseDisease (Malaria)
Mosquito
S
O
SB1
DDT in Breast Milk
S
S
R2
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Impact of DDT on Malaria 3
DDT UseDisease (Malaria)
Mosquito
S
O
SB1
DDT in Breast Milk
S
S
R2
DDT Accumulation inGecko (Lizard)
# Cat
# Rat
S
OO
S
R3
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http://butane.chem.uiuc.edu/pshapley/Environmental/L37/1.html
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Impact of DDT on Malaria 4
DDT UseDisease (Malaria)
Mosquito
S
O
SB1
DDT in Breast Milk
S
S
R2
DDT Accumulation inGecko (Lizard)
# Cat
# Rat
S
OO
S
R3
# Parasitic Wasp
# Caterpillar
# Thatch Roof Eatenand Destroyed
O
O
S
S
S
R4R5
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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
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Economy and Population 1
• Sherwood (2002, pp.241-262)
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Economy and Population 2
• Sherwood (2002, pp.241-262)
Deaths
Population
Births
Death Rate
Birth Rate
O
S
S
S
S
S
R2
B1
Disease
S
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Economy and Population 3
• Sherwood (2002, pp.241-262)
Deaths
Population
Births
Death Rate
Birth Rate
O
S
S
S
S
S
R2
B1
Disease
S
Economic Activity
Desire for Wealth
S
S
38
Economy and Population 4
• Sherwood (2002, pp.241-262)
Deaths
Population
Births
Death Rate
Birth Rate
O
S
S
S
S
S
R2
B1
Disease
S
Economic Activity
Desire for Wealth
S
S
Resource Consumption
Pollution
S
S
S
B3
39
Economy and Population 5
• Sherwood (2002, pp.241-262)
Deaths
Population
Births
Death Rate
Birth Rate
O
S
S
S
S
S
R2
B1
Disease
S
Economic Activity
Desire for Wealth
S
S
Resource Consumption
Pollution
S
S
S
B3
Competition forScarce Resources
Resource Capacity
Famine
War
O
SS
SS
S
B5
B4
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Economy and Population 6
41
Economy and Population 7
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Common Pool Resources
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Corruption System