L2-SD Systems Thinking & Causal Loop Diagramming.ppt

7/22/2019 L2-SD Systems Thinking & Causal Loop Diagramming.ppt

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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



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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



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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

??



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

??



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:



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.




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



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.



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

+

-

+

-



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



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)




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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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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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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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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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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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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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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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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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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More Examples of Negative Feedback Loops

Hunger

FoodConsumption

( + )

( - )

( - )

Bodytemperature

Sweat ( + )

( - )

( - )

Foxpopulation

Harepopulation

( + )

( - )

( - )

Badbehavior

Punishment ( + )

( - )

( - ) ?


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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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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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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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Taking a Shower: The Movie


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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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Managing Water T in a Shower

Water

Temperature

T GapTap setting

Desired

Temperature

S

O

S

(A-D)

B


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System Dynamics:

The Cartoon

EXERCISES : Develop causal loop diagrams from the following verbal


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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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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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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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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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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

Documents

L2-SD Systems Thinking & Causal Loop Diagramming.ppt