142
Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Embed Size (px)

Citation preview

Page 1: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Systems Thinking, System Dynamics, Simulation

James R. BurnsSummer 2009

Page 2: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Course Content Structure—see Syllabus• Systems Thinking• System Dynamics• Continuous Deterministic Simulation

– VENSIM

• Goldratt• Discrete Stochastic Simulation

– PROMODEL

Page 3: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Our web site

• http://burns.ba.ttu.edu/ba_7000.htm

Page 4: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Goals of this course…

• To learn Senge’s five disciplines• How to build a learning organization• How to challenge mental models• Master the seven laws of systems thinking• Understand the principle of leverage

• To learn the basics of causal modeling– known as Causal Loop Diagramming, CLD

Page 5: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Senge’s Five Disciplines

• Personal Mastery• because we need to be the very best we can be

• Mental Models• because these are the basis of all decision-making

• Shared Vision• because this galvanizes workers to pursue a

common goal

• Team Learning• because companies are organized into teams

• Systems Thinking• because this is only tool for coping with complexity

Page 6: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

More Goals of this course….

• To learn how transfer CLD’s to Stock & Flow Diagrams, SFDs

• To learn how to implement SFD’s in VENSIM

• To learn how to parameterize a VENSIM model

• To learn how to validate a VENSIM model• To learn how to conduct what-if

experiments• To do sensitivity studies

Page 7: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

How do these goals align with your…• goals for the course• expectations for the course in

general?

Page 8: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Would you like to ….

• learn about the Archetypes• learn how to recognize and apply

the Archetypes

Page 9: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

What kinds of processes, systems?• Dynamics of charisma• Agricultural processes• Project management• Enronitus• Growth and over-investment• WHAT ELSE?Project proposal is due July 9 (Friday)

Page 10: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Requirements for Completion• Midterm worth 30%• Final worth 30%• Homework worth 10%• Term project worth 20%• Presentation worth 5%• Class participation worth 5%

Page 11: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Pace

• More relaxed• No ties• Driven more by the needs of the

students

Page 12: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Grades??!!

• If you satisfactorily complete all the work required in this course, you will get at least a B– My guarantee– If you turn in unsatisfactory work, I

will ask you to redo it

• To get an A you must have a course grade above 89.999

Page 13: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Term Project

• You get to choose the topic• Topic is due on 7-9• Will ask you to turn-in as

homework your– Causal loop diagram– Stock-and-flow diagram

Page 14: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Definitions and Terms• ST--Systems Thinking• SD--Systems Dynamics• CLD--Causal Loop Diagram• BOT--Behavior Over Time Chart• SFD--Stock & Flow Diagram

– Also called Forrester Schematic, or simply “Flow Diagram”

• quantity--any variable, parameter, constant, or output

• edge--a causal link between quantities

Page 15: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Senge’s Five Disciplines

• Personal Mastery• because we need to be the very best we can be

• Mental Models• because these are the basis of all decision-making

• Shared Vision• because this galvanizes workers to pursue a

common goal

• Team Learning• because companies are organized into teams

• Systems Thinking• because this is only tool for coping with complexity

Page 16: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

System Dynamics Software• STELLA and I think

– High Performance Systems, Inc.– best fit for K-12 education

• Vensim– Ventana Systems, Inc.– Free from downloading off their web site:

www.vensim.com– Robust--including parametric data fitting and

optimization– best fit for higher education

• PowerSim– What Arthur Andersen is using

Page 17: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

What is system dynamics?

• A way to characterize systems as stocks and flows between stocks

• Stocks are variables that accumulate the affects of other variables

• Rates are variables the control the flows of material into and out of stocks

• Auxiliaries are variables the modify information as it is passed from stocks to rates

Page 18: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

A Simple Methodology

• Collect info on the problem• List variables on post-it notes• Describe causality using a CLD• Translate CLD into SFD• Enter into VENSIM• Perform sensitivity and validation studies• Perform policy and WHAT IF experiments• Write recommendations

Page 19: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Causal Modeling

• A way to characterize the physics of the system

• Lacking: a Newton to describe the causality in these socioeconomic systems

Page 20: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Key Benefits of the ST/SD

• A deeper level of learning– Far better than a mere verbal description

• A clear structural representation of the problem or process

• A way to extract the behavioral implications from the structure and data

• A “hands on” tool on which to conduct WHAT IF

Page 21: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Reinforcing Loop: Structure

Growth rate

Population

Sales

SatisfiedCustomers

Positive word ofmouth

Page 22: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Reinforcing Loop: Behavior

Population

20 B

10 B

0

0 20 40 60 80 100 120 140 160 180 200Time (Year)

Population : pop1Population : Current

Page 23: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Balancing Loop: Structure

DesiredInventory

Actualinventory

Inventorygap

Order rate

O B

Page 24: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Balancing Loop: Behavior

Inventory

1,000

500

0

0 10 20 30 40 50 60 70 80 90 100Time (Month)

Inventory : inv1

Page 25: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Stock and Flow Notation--Quantities• STOCK

• RATE

• Auxiliary

Stock

Rate

i1

i2

i3

Auxiliary

o1

o2

o3

Page 26: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Stock and Flow Notation--Quantities• Input/Parameter/Lookup

• Have no edges directed toward them

• Output• Have no edges directed away from them

i1

i2

i3

Auxiliary

o1

o2

o3

Page 27: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Inputs and Outputs

• Inputs• Parameters• Lookups

• Outputs

Input/Parameter/Lookup

a

b

c

Page 28: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Stock and Flow Notation--edges• Information

• Flow

a b

x

Page 29: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Some rules for translating CLD’s into SFD’s• There are two types of causal links in

causal models (but we don’t distinguish between them)– Information– Flow

1.Information proceeds from stocks and parameters/inputs toward rates where it is used to control flows

2.Flow edges proceed from rates to states (stocks) in the causal diagram always

Page 30: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Systems Thinking basics

• Having established two basic loop types—reinforcing and balancing—let us proceed to a discussion of archetypes

• Archetypes use the basic reinforcing and balancing loops

Page 31: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Nature’s Templates: the Archetypes• Structures of which we are

unaware hold us prisoner• The swimmer scenario

• Certain patterns of structure occur again and again: called ARCHETYPES

Page 32: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

We are creating a “language”

• reinforcing feedback and balancing feedback are like the nouns and verbs

• systems archetypes are the basic sentences• Certain behavior patterns appear again in

all disciplines--biology, psychology, family therapy, economics, political science, ecology and management

• Can result in the unification of knowledge across all fields

Page 33: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Recurring behavior patterns• Do we know how to recognize

them?• Do we know how to describe them?• Do we know how to prescribe cures

for them?• The ARCHETYPES describe these

recurring behavior patterns

Page 34: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

The ARCHETYPES • Provide leverage points, intervention

junctures at which substantial change can be brought about

• Put the systems perspective into practice• About a dozen systems ARCHETYPES

have been identified• All ARCHETYPES are made up of the

systems building blocks: reinforcing processes, balancing processes, delays

Page 35: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

As mentioned, before attacking the ARCHETYPES we need to understand simple structures

• The reinforcing feedback loop• The balancing feedback loop

Page 36: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

ARCHETYPE 1: LIMITS TO GROWTH• A reinforcing process is set in motion

to produce a desired result. It creates a spiral of success but also creates inadvertent secondary effects (manifested in a balancing process) that eventually slow down the success.

• All growth will eventually run up against constraints, impediments

Page 37: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Management Principle relative to ARCHETYPE 1• Don’t push growth or success;

instead, remove the factors limiting growth

Page 38: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

ARCHETYPE 1: LIMITS TO GROWTH• Useful in all situations where

growth bumps up against limits• Firms grow for a while, then plateau• Individuals get better for a while,

then their personal growth slows.• Falling in love is kind of like this

• The love begins to plateau as the couple get to know each other better

Page 39: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Structure

state of stockgrowing action slowing action

BalancingReinforcing

Page 40: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Understanding the Structure• High-tech orgs grow rapidly

because of their ability to introduce new products

• This growth plateaus as lead times become too long

Page 41: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

How to achieve Leverage

• Most managers react to the slowing growth by pushing harder on the reinforcing loop

• Unfortunately, the more vigorously you push the familiar levels, the more strongly the balancing process resists, and the more futile your efforts become.

• Instead, concentrate on the balancing loop--changing the limiting factor

• This is akin to Goldratt’s Theory of Constraints--remove the bottleneck, the impediment

Page 42: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Applications to Quality Circles and JIT• Quality circles work best when there is

even-handed emphasis on both balancing and reinforcing loops

• JIT has had to focus on recalcitrant suppliers

• THERE WILL ALWAYS BE MORE LIMITING PROCESSES

• When one source of limitation is removed, another will surface

• Growth eventually WILL STOP

Page 43: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Create your own LIMITS TO GROWTH story• Identify a limits to growth pattern

in your own experience• Diagram it

– What is growing– What might be limitations– Example--the COBA and University

capital campaigns– NOW, LOOK FOR LEVERAGE

Page 44: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Test your LIMITS TO GROWTH model• Talk to others about your

perception• Test your ideas about leverage in

small real-life experiments• Run and re-run the simulation

model• Approach possible resistance and

seek WIN-WIN strategies with them

Page 45: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

ARCHETYPE 2: shifting the burden

• An underlying problem generates symptoms that demand attention. But the underlying problem is difficult for people to address, either because it is obscure or costly to confront. So people “shift the burden” of their problem to other solutions--well-intentioned, easy fixes that seem extremely efficient.

Page 46: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Shifting the burden scenario, continued• Unfortunately, the easier solutions

only ameliorate the symptoms; they leave the underlying problem unaltered. The underlying problem grows worse and the system loses whatever abilities it had to solve the underlying problem.

Page 47: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

The Stereotype Structure

Problem

Symptomatic Solution

Fundamental Solution

Side effect

BALANCING

BALANCING

REINFORCING

Symptom-CorrectingProcess

Problem-Correcting Process

Addiction Loop

Page 48: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Special Case: Eroding Goals• Full employment meant 4%

unemployment in the 1960s, but 6 to 7% unemployment in the early 1980’s

• Gramm-Rudman bill called for reaching a balanced budget by 1991, but this was shifted to 1993 and from 1993 to 1996 and from 1996 to 1997

• “If all else fails, lower your goals..”

Page 49: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

EXAMPLE

Alcohol

Stress/Depression

Reduce workload

Health

BALANCING

BALANCING

Alcohol

Stress/Depression

Reduce workload

Health

BALANCING

BALANCING

Page 50: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Another Example

Costs of Higher Ed not funded by State or Students

Raise tuition, add course fees, etc.

Lower enrollments

Perceived cost to the student

Page 51: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Still Another ExampleHeroics and Overtime

Project Delayed

Efectiveness of PM practices

Reward for heroic behavior

Improvement of processes/practices

Symptom-correctingprocess

Problem-correctingProcess

Addiction Loop

Page 52: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Still other Problems

• What about retention of students• The perceived fix is raise the

admission standards• What about drug-related crime• The perceived fix is to remove the

drugs from the street

Page 53: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

“Shifting the Burden” is an insidious problem• Is has a subtle reinforcing cycle• This increases dependence on the

symptomatic solution• But eventually, the system loses

the ability to apply the fundamental solution

• The system collapses

Page 54: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Senge Says

• Today’s problems are yesterday’s solutions

• We tend to look for solutions where they are easiest to find

• The easy way out usually leads back in

Page 55: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

HOW TO ACHIEVE LEVERAGE• Must strengthen the fundamental

response– Requires a long-term orientation and

a shared vision

• Must weaken the symptomatic response– Requires a willingness to tell the truth

about these “solutions”

Page 56: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Create your own “Shifting the Burden” Story

• Is there a problem that is getting gradually worse over the long term?

• Is the health of the system gradually worsening?

• Is there a growing feeling of helplessness?• Have short-term fixes been applied?

• The local Mexican restaurant problem of using coupons to generate business and then can’t get away from using the coupons because their customer base is hooked on coupons

Page 57: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

To structure your problem

• Identify the problem• Next, identify a fundamental

solution• Then, identify one or several

symptomatic solutions• Finally, identify the possible

negative “side effects” of the symptomatic solution

Page 58: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Review

• We have now seen two of the basic systems archetypes. – The Limits to Growth Archetype– The Shifting the Burden Archetype

• As the archetypes are mastered, they become combined into more elaborate systemic descriptions.

• The “sentences” become parts of paragraphs• The simple stories become integrated into

more involved stories

Page 59: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Robust Loops

• In any loop involving a pair of quantities/edges,

• one quantity must be a rate• the other a state or stock, • one edge must be a flow edge• the other an information edge

Page 60: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

CONSISTENCY

• All of the edges directed toward a quantity are of the same type

• All of the edges directed away from a quantity are of the same type

Page 61: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Rates and their edges

q1

q2

q3

RATES

q4

q5

q6

Informationedges

Flow edges

Page 62: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Parameters and their edges

PARAMETER

q1

q2

q3

Informationedges

Page 63: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Stocks and their edges

q1

q2

q3

STOCK

q4

q5

q6

Flow edges Information edges

Page 64: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Auxiliaries and their edges

AUXILIARY

q1

q2

q3

q4

q5

q6

Informationedges

Informationedges

Page 65: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Outputs and their edges

OUTPUT

q1

q2

q3

Informationedges

Page 66: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

STEP 1: Identify parameters• Parameters have no edges

directed toward them

Page 67: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

STEP 2: Identify the edges directed from parameters• These are information edges

always

Page 68: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

STEP 3: By consistency identify as many other edge types as you can

Page 69: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

STEP 4: Look for loops involving a pair of quantities only• Use the rules for robust loops

identified above

Page 70: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

q1

q2

q3 q4

q5

q6

q7

q8

Page 71: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

q3

q6

q2

q7

q1

q4

q5 q8

Page 72: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Distinguishing Stocks & Flows by NameNAME UNITS

Stock or flow• Revenue• Liabilities• Employees• Depreciation• Construction starts• Hiring• material standard of living

Page 73: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

The VENSIM User Interface

• The Time bounds Dialog box

Page 74: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009
Page 75: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009
Page 76: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009
Page 77: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

A single-sector exponential growth model• Einstein said the most powerful

force in the world was compound interest

• interest taken in relation to principal

• Each stock requires an initial valueinterest prinicipal

Interest rate

R

Principal

Interest

Interest rate

Page 78: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Let’s DO IT

• Create the stock principal• Include the rate interest• Include the information connector• Initialize the stock• Simulate

Page 79: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

John vs. Jack

• Each works for 30 years before retiring• John makes $2000 contributions to his IRA

each year for the first five years and none there after.

• Jack makes $2000 contributions to his IRA each year beginning in year six and continuing through year 30

• Each IRA yields a 15% compounded return• Which turns out to be larger?

Page 80: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

John vs. Jack--two interest accounts.mdl

Principal

Interest

Interest rate

Principal 0

Interest 0

Interest rate 0

contributions

contributions 0

<Time>

John

Jack

Page 81: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

John vs. Jack

800,000

400,000

0

0 6 12 18 24 30Time (Year)

Principal : int1Principal 0 : int1

Page 82: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Contributions of John vs. those of Jack

2,050

1,525

1,000

475

-50

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30Time (Year)

contributions : int1contributions 0 : int1

Page 83: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Another single-sector Exponential growth Model• Consider a simple population with infinite

resources--food, water, air, etc. Given, mortality information in terms of birth and death rates, what is this population likely to grow to by a certain time.

• A population of 200,000, growing at 1.3% a year.

• A population of 1.6 billion with a birth rate norm of .04 and a death rate norm of .028

Page 84: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Experiments with growth models• Models with only one rate and one

state• Average lifetime death rates• Models in which the exiting rate is

not a function of its adjacent state

Page 85: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Example:

• Build a model of work flow from work undone to work completed.

• This flow is controlled by a “work rate.” • Assume that are 1000 days of undone

work• Assume the work rate is 20 completed

days a month• Assume the units on time are months• Assume no work is completed initially.

Page 86: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Solving the problem of negative stock drainage• pass information to the outgoing

rate• use the IF THEN ELSE function

Page 87: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Shifting loop Dominance• Rabbit populations grow rapidly with a

reproduction fraction of .125 per month• When the population reaches the carrying

capacity of 1000, the net growth rate falls back to zero, and the population stabilizes

• Starting with two rabbits, run for 100 months with a time step of 1 month

• (This model has two loops, an exponential growth loop (also called a reinforcing loop) and a balancing loop)

Page 88: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Shifting loop Dominance• Assumes the following relation for Effect of

Resources• Effect of Resources = (carrying capacity -

Rabbits)/carrying capacity• This is a multiplier• Multipliers are always dimless (dimensionless)• When rabbits are near zero, this is near 1• When rabbits are near carrying capacity, this is

near zero– This will shut down the net rabbit birth rate

Page 89: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

RabbitsNet Rabbit Birth rate

Effect of resourcesCarrying capacity

Normal Rabbit Growth Rate

B

R

Page 90: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Rabbits

1,00040

00

0 20 40 60 80 100Time (Month)

Rabbits : rab1Net Rabbit Birth rate : rab1

Page 91: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Dimensionality Considerations• VENSIM will check for dimensional

consistency if you enter dimensions• Rigorously, all models must be

dimensionally consistent• What ever units you use for stocks,

the associated rates must have those units divided by TIME

• An example follows

Page 92: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Cascaded rate-state (stock) combinations• In the oil exploration industry, unproven

reserves (measured in barrels) become proven reserves when they are discovered. The extraction rate transforms proven reserves into inventories of crude. The refining rate transforms inventories of crude into refined petroleum products. The consumption rate transforms refined products into pollution (air, heat, etc.)

Page 93: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Another cascaded rate-stock combination• Population cohorts. Suppose

population is broken down into age cohorts of 0-15, 16-30, 31-45, 46-60, 61-75, 76-90

• Here each cohort has a “lifetime” of 15 years

• Again, each rate has the units of the associated stocks divided by time

Page 94: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

A single-sector Exponential goal-seeking Model• Sonya Magnova is a resources planner

for a school district. Sonya wishes to a maintain a desired level of resources for the district. Sonya’s new resource provision policy is quite simple--adjust actual resources AR toward desired resources DR so as to force these to conform as closely as possible. The time required to add additional resources is AT.

Page 95: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

The Sector Approach to the Determination of Structure• What is meant by “sector?”• What are the steps

– to determination of structure within sectors

– to determination of structure between sectors

Page 96: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Definition of sector

• All the structure associated with a single flow

• Note that there could be several states associated with a single flow– The next sector in the pet population

model has three states in it

Page 97: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Sector Methodology, Overall• Identify flows (sectors) that must

be included within the model• Develop the structure within each

sector of the model. – Use standard one-sector sub-models

or develop the structure within the sector from scratch using the steps in Table 15.5

Page 98: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Sector Methodology, Overall Cont’d• Develop the structure between all

sectors that make up the model• Implement the structure in a

commercially available simulation package

Page 99: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Steps Required to Formulate the Structure for a Sector from Scratch• Specify the quantities required to

delineate the structure within each sector

• Determine the interactions between the quantities and delineate the resultant causal diagram

• Classify the quantity and edge types and delineate the flow diagram

Page 100: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

• Resource, facility and infrastructure (desks, chairs, computers, networks, labs, etc.) needs for an educational entity are driven by a growing population that it serves. Currently, the population stands at 210,000 and is growing at the rate of two percent a year. One out of every three of these persons is a student.

• One teacher is needed for every 25 students. Currently, there are 2,300 actual teachers; three percent of these leave each year. Construct a structure for each that drives the actual level toward the desired level. Assume an adjustment time of one year. Set this up in VENSIM to run for 25 years, with a time-step of .25 years.

Page 101: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

• One teacher is needed for every 25 students. One-hundred square feet of facility space is needed for each student. Thirty-five hundred dollars in infrastructure is needed for each student. Currently, there are 2,300 teachers; three percent of these leave each year. Currently, there is five million sq. ft of facility space, but this becomes obsolescent after fifty years. Currently, there is $205,320,000 in infrastructure investment, but this is fully depreciated after ten years. For each of infrastructure, teachers and facility space, determine a desired level or stock for the same. Construct a structure for each that drives the actual level toward the desired level.

Page 102: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

• Set this up in VENSIM to run for 25 years, with a time-step of .25 years. Assume adjustment times of one year. DETERMINE HOW MUCH IN THE WAY OF FACILITIES, TEACHERS AND INFRASTRUCTURE ARE NEEDED PER YEAR OVER THIS TIME PERIOD.

Page 103: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

What are the main sectors and how do these interact?• Population• Teacher resources• Facilities• Infrastructure

Page 104: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Factors affecting teacher departures• Inside vs. outside salaries• Student-teacher ratios• How might these affects be

included?

Page 105: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Teacher departure description• It is known that when the ratio of average

“inside the district” salary is comparable to outside salaries of positions that could be held by teachers, morale is normal and teacher departures are normal

• When the inside-side salary ratio is less than one, morale is low and departures are greater than normal

• The converse is true as well

Page 106: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Teacher departure description• When student-teacher ratios

exceed the ideal or desired student teacher ratio, which is twenty four, morale is low and again departures are greater than normal

• The converse is true as well

Page 107: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

A Two-sector Housing/population Model• A resort community in Colorado has

determined that population growth in the area depends on the availability of housing as well as the persistent natural attractiveness of the area. Abundant housing attracts people at a greater rate than under normal conditions. The opposite is true when housing is tight. Area Residents also leave the community at a certain rate due primarily to the availability of housing.

Page 108: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Two-sector Population/housing Model, Continued• The housing construction industry, on the

other hand, fluctuates depending on the land availability and housing desires. Abundant housing cuts back the construction of houses while the opposite is true when the housing situation is tight. Also, as land for residential development fills up (in this mountain valley), the construction rate decreases to the level of the demolition rate of houses.

Page 109: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

What are the main sectors and how do these interact?• Population• Housing

Page 110: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

What is the structure within each sector?• Determine state/rate interactions

first• Determine necessary supporting

infrastructure– PARAMETERS– AUXILIARIES

Page 111: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

What does the structure within the population sector look like?• RATES: in-migration, out-

migration, net death rate• STATES: population• PARAMETERS: in-migration normal,

out-migration normal, net death-rate normal

Page 112: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

What does the structure within the housing sector look like?• RATES: construction rate, demolition rate• STATES: housing• AUXILIARIES: Land availability multiplier,

land fraction occupied• PARAMETERS: normal housing

construction, average lifetime of housing• PARAMETERS: land occupied by each unit,

total residential land

Page 113: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

What is the structure between sectors?• There are only AUXILIARIES,

PARAMETERS, INPUTS and OUTPUTS

Page 114: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

What are the between-sector auxiliaries?• Housing desired• Housing ratio• Housing construction multiplier• Attractiveness for in-migration

multiplier• PARAMETER: Housing units

required per person

Page 115: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Nature’s Templates: the Archetypes• Structures of which we are

unaware hold us prisoner• The swimmer scenario

• Certain patterns of structure occur again and again: called ARCHETYPES

Page 116: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

We are creating a “language”• reinforcing feedback and balancing

feedback are like the nouns and verbs• systems archetypes are the basic

sentences• Behavior patterns appear again in all

disciplines--biology, psychology, family therapy, economics, political science, ecology and management

• Can result in the unification of knowledge across all fields

Page 117: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Recurring behavior patterns• Do we know how to recognize

them?• Do we know how to describe them?• Do we know how to prescribe cures

for them?• The ARCHETYPES describe these

recurring behavior patterns

Page 118: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

The ARCHETYPES

• provide leverage points, intervention junctures at which substantial change can be brought about

• put the systems perspective into practice• About a dozen systems ARCHETYPES

have been identified• All ARCHETYPES are made up of the

systems building blocks: reinforcing processes, balancing processes, delays

Page 119: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Before attacking the ARCHETYPES we need to understand simple structures• the reinforcing feedback loop• the balancing feedback loop• THE DEMO

Page 120: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

ARCHETYPE 1: LIMITS TO GROWTH• A reinforcing process is set in

motion to produce a desired result. It creates a spiral of success but also creates inadvertent secondary effects (manifested in a alancing process) that eventually slow down the success.

Page 121: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Management Principle relative to ARCHETYPE 1• Don’t push growth or success;

remove the factors limiting growth

Page 122: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

ARCHETYPE 1: LIMITS TO GROWTH• Useful in all situations where

growth bumps up against limits• Firms grow for a while, then plateau• Individuals get better for a while,

then their personal growth slows.• Falling in love is kind of like this

• The love begins to plateau as the couple get to know each other better

Page 123: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Structure

state of stockgrowing action slowing action

BalancingReinforcing

Page 124: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Understanding the Structure• High-tech orgs grow rapidly

because of ability to introduce new products

• This growth plateaus as lead times become too long

Page 125: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

How to achieve Leverage

• Most managers react to the slowing growth by pushing harder on the reinforcing loop

• Unfortunately, the more vigorously you push the familiar levels, the more strongly the balancing process resists, and the more futile your efforts become.

• Instead, concentrate on the balancing loop--changing the limiting factor

• This is akin to Goldratt’s Theory of Constraints--remove the bottleneck, the impediment

Page 126: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Applications to Quality Circles and JIT• Quality circles work best when there is

even-handed emphasis on both balancing and reinforcing loops

• JIT has had to focus on recalcitrant suppliers

• THERE WILL ALWAYS BE MORE LIMITING PROCESSES

• When once source of limitation is removed, another will surface

• Growth eventually WILL STOP

Page 127: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Create your own LIMITS TO GROWTH story• Identify a limits to growth pattern

in your own experience• Diagram it

– What is growing– What might be limitations– Example--the COBA and University

capital campaigns– NOW, LOOK FOR LEVERAGE

Page 128: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Test your LIMITS TO GROWTH model• Talk to others about your

perception• Test your ideas about leverage in

small real-life experiments• Run and re-run the simulation

model• Approach possible resistance and

seek WIN-WIN strategies with them

Page 129: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

ARCHETYPE 2: shifting the burden• An underlying problem generates symptoms that

demand attention. But the underlying problem is difficult for people to address, either because it is obscure or costly to confront. So people “shift the burden” of their problem to other solutions--well-intentioned, easy fixes that seem extremely efficient. Unfortunately the easier solutions only ameliorate the symptoms; they leave the underlying problem unaltered. The underlying problem grows worse and the system loses whatever abilities it had to solve the underlying problem.

Page 130: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

The Stereotype Structure

Problem

Symptomatic Solution

Fundamental Solution

Side effect

BALANCING

BALANCING

REINFORCING

Symptiom-CorrectingProcess

Problem-Correcting Process

Addictioin Loop

Page 131: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Special Case: Eroding Goals• Full employment meant 4%

unemployment in the 60’s, but 6 to 7% unemployment in the early 1980’s

• Gramm-Rudman bill called for reaching a balanced budget by 1991, but this was shifted to 1993 and from 1993 to 1996 and from 1996 to 1998

• “If all else fails, lower your goals..”

Page 132: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

EXAMPLE

Alcohol

Stress/Depression

Reduce workload

Health

BALANCING

BALANCING

Alcohol

Stress/Depression

Reduce workload

Health

BALANCING

BALANCING

Page 133: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Another Example

Costs of Higher Ed not funded by State

Raise tuition, add course fees, etc.

Lower enrollments

Perceived cost to the student

Page 134: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Still Another Example

Heroics and Overtime

Project Delayed

Efectiveness of PM practices

Reward for heroic behavior

Improvement of processes/practices

Symptom-correctingprocess

Problem-correctingProcess

Addiction Loop

Page 135: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

“Shifting the Burden” is an insidious problem• Is has a subtle reinforcing cycle• This increases dependence on the

symptomatic solution• But eventually, the system loses

the ability to apply the fundamental solution

• The system collapses

Page 136: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Senge Says

• Today’s problems are yesterday’s solutions

• We tend to look for solutions where they are easiest to find

Page 137: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

HOW TO ACHIEVE LEVERAGE• Must strengthen the fundamental

response– Requires a long-term orientation and

a shared vision

• Must weaken the symptomatic response– Requires a willingness to tell the truth

about these “solutions”

Page 138: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Create your own “Shifting the Burden” Story• Is there a problem that is getting

gradually worse over the long term?• Is the overall health of the system

gradually worsening?• Is there a growing feeling of helplessness?• Have short-term fixes been applied?

• The Casa Olay problem of using coupons to generate business and then can’t get away from using the coupons because their customer base is hooked on coupons

Page 139: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

To structure your problem

• Identify the problem• Next, identify a fundamental

solution• Then, identify one or several

symptomatic solutions• Finally, identify the possible

negative “side effects” of the symptomatic solution

Page 140: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Review

• We have now seen two of the basic systems archetypes. – The Limits to Growth Archetype– The Shifting the Burden Archetype

• As the archetypes are mastered, they become combined into more elaborate systemic descriptions.

• The basic “sentences” become parts of paragraphs

• The simple stories become integrated into more involved stories

Page 141: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009

Seeing Structures, not just Trees• Helps us focus on what is

important and what is not• Helps us determine what variables

to focus on and which to pay less attention to

Page 142: Systems Thinking, System Dynamics, Simulation James R. Burns Summer 2009