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Simulation & Modeling Week 3 Causal Loop Diagrams 1
Systems Thinking & Causal Loop
Diagramming
Simulation and Modeling
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Concepts of Systems Thinking
System Definitions :
A collection of interacting elements that function together for
some purpose.
a group of interacting parts that share a common location in
space, time and/or function
The systems approach is the study of systems that emphasises
the connections among various parts that constitute a whole.
Systems thinking is concerned with connectedness as well as
wholeness in problem analysis and solving.[Source: Senge, 1993]
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A new way of thinking
Emerging new way of thinking about business process that
Provides deeper understanding of inter relationships within anorganisation and how all main aspects contribute to achieve
organisational whole.
Appreciates both role of systems thinking and use of systemdynamics notation
Uses systemic approach in corporate strategic planning andcontrol
Simulation & Modeling Week 3 Causal Loop Diagrams 3
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What is System Thinking
Systems thinking is the art and science ofmaking reliable influences about behaviour
by developing an increasingly deeperunderstanding of underlying structure.
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Thinking in Circles
Abdel-Hamids article Thinking in Cycles states that...(with) the rapid evolution of software engineering tools,techniques, and technology, managers must be prepared
to boldly go where no one has gone before while virtuallyguaranteeing that their missions will meet with success.
Similarly redesigning or re-engineering Business
processes or investing in new technology is going toplaces where organisations have not been before!
[Source: Abdel-Hamid, 1991]
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System dynamics is a powerful, yet simple, methodology for developing
deep insights into the working of various systems and providingmicroworlds for policy design.
Over the years, system dynamics has emerged as one of the most
powerful methodologies of social systems analysis and design.
Supports modelling Dynamic Behaviour:
Instances, Causes and Problems
Feed back loops and delays Influence Diagrams Construction and Use
Systems Modelling using:
Influence Diagrams:
Stock and Flow diagrams
System Thinking and System Dynamics
Simulation & Modeling Week 3 Causal Loop Diagrams 6
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Where does cause arise? Aristotelian causality
4 types of cause contribute explain a phenomenon 1. Material cause: the substance that made it so
2. Efficient cause: the direct efforts that made it so
3. Formal cause: the plan or agent that made it so 4. Final cause: the ultimate purpose for being so
??
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Where does cause arise? Aristotelean causality
e.g. Why does a house exist? 1. Material cause: wood, bricks, mortar
2. Efficient cause: the construction workers
3. Formal cause: the blue prints 4. Final cause: need for a house
??
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Where does cause arise?
e.g. Community living next to an old paint factory is discovered tosuffer from prevalence of lead poisoning
1. Material cause:
2. Efficient cause:
3. Formal cause: 4. Final cause:
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Challenge Cause
GLOBAL
natural resource depletion Human consumption
Global warming and climate change Release of carbon from fossil fuels
Overpopulation Reproductive rights
REGIONAL
Air pollution Automobile
Species loss
Stream & lake pollution Agriculture and industry
Deforestation Overpopulation, demand
Erosion/desertification Industrialized agriculture
Lack or agricultural diversity Societies demands
Environmental damage of war War
Acid rain industryLOCAL
Suburban sprawl Lack of planning (transportation)
Sewer overflows pollution Impermeable surfaces
Waste/landfill Lack of recycling, lack of information
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System Thinking Diagrams (STDs)(Causal loop Diagrams (CLDs)
Systems Thinking Diagrams are composed of only two components,
elements and influences.
An influence also has a direction, indicated by an arrow, and an
indicator as to whether the influenced element is changed in the same(S) or opposite (O) direction as the influencing element.
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Use of Influence Diagrams
Influence diagrams are also known as causal-loop diagrams.A link from A to B is positive if a change in A produces a change
in the same direction.
A link from A to B is negative if a change in A produces achange in B in the opposite direction. The direction of an arrow
shows the direction of causation/Causality.
It SHOULD incorporate the principal performance influencesof the system under study.
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What are Causal Loop Diagrams (CLD) ?
Casual Loop Diagrams are cause and effect representations ofstructures and processes that have loops or feedback. Causal loop diagrams show causality There is an arrow going from population to death
population deaths
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Causal Links
C D
A B+ A influences B. If Aincreases, that will tend
to increase B. If A goes
down in value, that will
tend to reduce B.
C influences D. If C
increases, that will tend
to decrease D. If C goes
down in value, that will
tend to increase D.
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Polarity
Polarity : We can associate a direction of influence or polarity + or s (same) indicates that an increase in the cause will lead to an
increase in the effect
- or o (opposite) indicates that positive value of the cause will lead to a
decrease in the effect
population deaths
deathspopulation
+
-
+
-
-
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Loops
A loop : occurs when arrows connect a variable to itselfthrough a series of other variables
This example shows a loop from population through births andback to population.
There exists both negative (balancing) and positive(Reinforcing) feedback loops in SD problems
population births
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Anatomy of a Causal Loop Diagram
HungerAmount
EatenB
O
S
The O means that the
two variables move in
opposite directions, all
other things being equal
The S means that the
two variables move in the
same direction, all other
things being equal
Nature of loop. Indicates
whether the loop is
balancing or reinforcing
Causal relationship
between two variables
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System Thinking Structures (Archetypes)
The basic idea of structure(s) is to point out the influence one thing has
on another. That is, how do things influence other things to change.If I have two things, thing 1 and thing 2, there are only two ways one can
influence the other.
As indicated in the diagram above, thing 1 can add to thing 2, as
indicated by a "+" sign, thus increasing thing 2.
The alternative is that thing 1 can subtract from thing 2, as indicated by
the "-" sign in the above figure, thus decreasing thing 2.
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Let us examine the most common example (production -inventory) Sales
adds to revenue. Even if sales decrease it will still add to revenue, just notquite as much as before.
On the other hand, if sales increases it will add even more to revenue.
The figure above indicates that product sales subtracts from finished goods
inventory. If product sales increase it will subtract even more from finished
goods inventory. On the other hand, if product sales decrease it will still
subtract from finished goods inventory, just not quite so much.
System Thinking Structures (Archetypes)
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Feedback is critical in systems view
Feedback: The returning of part of the output of a system to bereintroduced as input (Websters) (+) feedback reinforces change
(-) feedback counteracts change
f(parts + feedback)=
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Reinforcing /Positive Feedback loops
A reinforcing loop is one in which the interactions are such that each
action adds to the other. Any situation where action produces a resultwhich promotes more of the same action is representative of a
reinforcing loop.
Examples : snow balls rolling down hill, population growth.
( + )
( + )
( + )
Population
size
Population
growth
Change leads to further change in samedirection
Growth enhancing
Potentially destablizing
Finite in extent
Vicious cycles, bandwagons, self-fulfillingprophecy
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Simulation & Modeling Week 3 Causal Loop Diagrams 22
Diagram shows what happens in
a typical savings account.
The principal in the savings
account interacts with the interest
rate and adds to the interest.
Interest rate is considered to be a
constant in this example. Interest
then adds to the principal.
This reinforcing action happensevery so many months depending
on the period over which the
institution computes the interest.
Reinforcing /Positive Feedback loops
The SNOWBALL rolling down hill isyour signal that the loop is a
reinforcing loop. The SMALL GRAPH
to the right of principle indicates that
the growth of principal is exponential.
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Simulation & Modeling Week 3 Causal Loop Diagrams 23
Reinforcing / Positive Feedback Loops
It is denoted byR or+ sign or with snow ball symbol. Positive tends to run away leading to situations that are out of control. Overall polarity of feedback loop is determined by counting the number of
links that are opposite.
An even number of opposite(-) links implies positive feedback and anodd numberof opposite links(-) implies negative feedback.
( + )
( + )
( + )
Beer
consumption
BeerNut
consumption
Interest BalanceR
S
The S
means that
the two
variables
move in the
same
direction, all
other things
being equal
Causal relationship
between two variables
S
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Simulation & Modeling Week 3 Causal Loop Diagrams 24
Phrases that characterize the phenomenon of feedback include : Snowball effect as it rolls down a mountain side, it picks up snow, its mass and
circumference increase which causes the snow ball to grow even faster
As a political movement grows, its popularity and ability to attract support also grows
The exponential growth curve characterizes most positive feedbacksystems. World population, food production, industrialization, pollution allexhibit exponential growth
Time
Variable
Reinforcing / Positive Feedback Loops
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Simulation & Modeling Week 3 Causal Loop Diagrams 25
Examples: Positive Feedback Loops
Industrial
Capital
Production
+
+
Invest-
ment+
( + )D C
A B
(+)
(+)
(+)
(+)
Plant A provides food that worm B uses
Worm B released nutrients that are then used by microbe C
Microbe C transfers nutrients to plant D
Plant D provides necessary shade for plant A
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Simulation & Modeling Week 3 Causal Loop Diagrams 26
More Examples of positive feedback
Bankbalance
Interestadded/month
( + )
( + )
( + )
Health conditions
Natural resources(natural capital)
Poverty anddesperation( - )
( - )
( + )
( + )
Middle classliving in urban core
Size oftax base
Quality ofpublic services
( + )
( + )
( + )
( + )
Humanpopulation
( + )
( + )
(+), if even # of (-) signs
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Simulation & Modeling Week 3 Causal Loop Diagrams 27
Economic Positive Loops
Industrial
Capital
Invest
ment
Sales
Profits
Advertising
Production
+
+
+
++
+
+
How many loops do we have ?
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Balancing / Negative Feedback loops
A balancing loop is one in which action attempts to bring two things to
agreement. Any situation where one attempts to solve a problem or achievea goal or objective is representative of a balancing loop.
Example : Self regulating temperature of the human body which enables it
to maintain a relatively constant internal temperature called homeostatis
Body
temperature
Sweat ( + )
( - )
( - )
Phrases that characterize thephenomenon of feedback include :
Self governing,
self regulating,
self equilibrating,
adaptive
all implying the presence of a
goal.Simulation & Modeling Week 3 Causal Loop Diagrams 28
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Simulation & Modeling Week 3 Causal Loop Diagrams 29
Negative Feedback Loops
This is a negative or balancing. It is denoted by B or - sign Positive tends to leads to a controlled equilibrium or steady state. Negative feedback loops exist when there are an odd number of negative
links in a loop.
The people there are, the more they die thus keeping the population low.
population deaths
+
-
( - )
-
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Simulation & Modeling Week 3 Causal Loop Diagrams 30
Desired state (goal) serves as areference on which the system basesaction and is determined externally.
Gap this is the discrepancy between thegoal and state of the system determined
the magnitude and direction of thecorrective action taken.
Action (rate)
System state (level).
To minimise the discrepancy (gap) , thesystem initiates action to decrease(increase) the level.
Negative Feedback Loops- Four Basic Elements
B l i /N i F db k l E l i
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Balancing/Negative Feedback loops - Explanation
The basic form of the balancing loop.
The desired state interacts with the current
state to produce a gap. The gap adds to theaction and the action adds to the current
state. The current state then subtracts from
the gap.
The small clock to the right of the arc
between action and current state indicates
some time delay that it takes for the action to
change the current state. As the current state
gets closer to the desired state the gap gets
smaller and smaller so it adds less and less tothe action,which is adding to the current state.
Once the action has moved the current state
to a point where it equals the desired state the
gap is zero and there's no more addition to the
action, so there is no more action.
The balance in the centre of the
loop is your indication that the loop is
a balancing loop.
Typical examples of balancing loops
are driving from location A to
location B, developing a skill,
building something, fixing a
problem, etc.
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Simulation & Modeling Week 3 Causal Loop Diagrams 32
More Examples of Negative Feedback Loops
Hunger
FoodConsumption
( + )
( - )
( - )
Bodytemperature
Sweat ( + )
( - )
( - )
Foxpopulation
Harepopulation
( + )
( - )
( - )
Badbehavior
Punishment ( + )
( - )
( - ) ?
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Simulation & Modeling Week 3 Causal Loop Diagrams 33
Example : Social Life CLD
hrs/week
together
average time
for new work
Quality of
work
# ofmistakes
time spent
correcting mistakes
+
+
-
-
# of
invitations
Desired
time together
+
+
-
+
-
pressure from boss
+
How many loops do we have ?
C l L Di i i
-
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Simulation & Modeling Week 3 Causal Loop Diagrams 34
Causal Loop Diagramming exercises
A good way to start is by brainstorming a list of all variables associatedwith a phenomenon.
Then, begin your causal loop diagram by selecting only those systemelements that are causally related to each other.
Arrows between variables are used to indicate the direction of causality.
For instance, if you have two variables, amount of coal burned andamount of acid rain generated an arrow would be directed from the coal tothe acid rain.
Points of arrows are labeled with (+) or (-) sign to indicate positive ornegative effect. A (+) means that change in the variable at the tail of the
arrow leads to change in the same direction in the variable at the point ofthe arrow (i.e., if the one at the tail increases, then this necessarily causesthe one at the point to increase). Important: when labeling, consider eachpair of variables connected by an arrow in isolation from all other variables(completely ignore the other variables).
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Simulation & Modeling Week 3 Causal Loop Diagrams 35
Causal Loop Diagramming exercises
Determine the overall sign of a feedback loop by counting thetotal number of (-) signs at the end of the arrows within thecomplete loop.
The loop is a positive feedbackif there is an even number of (-) signs
(or no - signs). The loop is a negative feedbackif there is an oddnumber of (-) signs.
Place a large (+) or (-) sign in the center of each loop to indicate
the overall direction. Both positive and negative loops aretypically embedded within large dynamic systems.
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Simulation & Modeling Week 3 Causal Loop Diagrams 36
Taking a Shower: The Movie
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Simulation & Modeling Week 3 Causal Loop Diagrams 37
Managing Water T in a Shower
22
24
26
28
30
32
34
0 10 20 30 40 50 60 70 80 90 100 110 120
Time
W
aterT
What do you think would happen in a more complicated setting,
where you have to share the supply of hot water (critical resource)
with someone/something else?
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Simulation & Modeling Week 3 Causal Loop Diagrams 38
Managing Water T in a Shower
Water
Temperature
T GapTap setting
Desired
Temperature
S
O
S
(A-D)
B
-
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Simulation & Modeling Week 3 Causal Loop Diagrams 39
System Dynamics:
The Cartoon
EXERCISES : Develop causal loop diagrams from the following verbal
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Simulation & Modeling Week 3 Causal Loop Diagrams 40
EXERCISES : Develop causal loop diagrams from the following verbal
descriptions giving clear explanations. Identify the relationships & polarity
between each pair of variables as well as the polarity of each loop
Population and Economic Growth Loop : As employment opportunities increasein a city, people are attracted into the urban area. However, in-migrants do not immediatelyswarm to employment opportunities in the area. Since migrants react to perceived
opportunity, the lag in acquiring information may cause 5 to 20 year delay in response.
Population growth from the influx of migrants tends to encourage business expansion in
the growing urban area. The additional economical expansion creates demand foradditional labor. This demand further increases employment opportunities in the area.
Population and Land Use Loop : While tending to reinforce economic growth,population growth tends to drive housing construction at a greater pace to match population
growth. Assuming only a fixed amount of land available for industrial and housing use,
increasing the housing stock makes less land available for business expansion. As theunavailability of more land begins to suppress business expansion in the area, the demand
for labour decreased. Consequently, local employment opportunities decline. Once
potential migrants perceive the lack of opportunities, declining in-migration generates a
reduction in the population growth of the area.
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Simulation & Modeling Week 3 Causal Loop Diagrams 41
Group Work : Rural Development
Form groups of 5
Draw a causal loop diagram showing the causal relationships and polarity
from the following variables (indicate delays where applicable)
Births
Population
Adult Women
Soil fertility
Social controls on children
Food/person
Intensity of Land use Food production
Quality of life
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Simulation & Modeling Week 3 Causal Loop Diagrams 42
1. Name your variables carefully. In particular, avoid names that alreadyimply directionality (e.g. amount of acid rain is an appropriate variable,
increase in acid rain is notappropriate). Generally your variables should
be nouns rather than verbs.
2. Confusion will inevitably result if you think about multiple arrowssimultaneously when labeling the end of an arrow. Focus only on thedirection and sign of causality in each pair. Then, when you are done
labeling each individual arrow, figure out the sign of the loop as a whole.
3. Arrows in causal loop diagrams do not necessarily represent flows of stuff
(material or energy). They represent flows of causality.
Tips : Drawing CLDs
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Simulation & Modeling Week 3 Causal Loop Diagrams 43
Examples
Middle classflight from cities
Decreasingtax base
Loss ofpublic services
( + )
( + )
( + )
( + )
Avoid using terms that indicate directionality e.g. flight from city
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Simulation & Modeling Week 3 Causal Loop Diagrams 44
If it helps to clarify dynamics, it is fine to include forcing variablesthat are cause, but are not themselves affected by the dynamics
depicted (i.e. they are not actually part of a loop within the
model).
As with all models, you should strive to use minimum number ofvariables necessary to capture the dynamics of interest. The first
draft of your causal loop diagram can generally be simplified inorder to increase clarity. Typically you will want to redraw your
model to make it as easy for others to interpret as possible.
Tips : Drawing CLDs
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Finding a cure for cancer at the cellular level will
not have a net benefit for
society if we are unable to deal with cancer at the
ecosystem level(e.g. population overgrowth, pollution, and so on).
Perhaps,
then, we are beginning to perceive diminishing
returns for reductionism and a swingback to a more unified science.
(Eugene Odum, 1913-2002)
Food for thought