tools for systems thinking and modeling

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Rockefeller College of Public Affairs and PolicyRockefeller College of Public Affairs and PolicyUniversity at AlbanyUniversity at Albany

Tools for Systems Thinkingand Modeling

Dynamics: Graphs over timeStructure: Causal-loop Diagrams

Stocks and Flows

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Events and DecisionsEvents and Decisions

Patterns of BehaviorPatterns of Behavior

System StructureSystem Structure

Reactive

Adaptive

Generative

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A Systems Perspective

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A systems view stands back just far enough to...• Deliberately blur discrete events into patterns of

behavior• Deliberately move from a focus on individual

decisions to a focus on policy structure

“Distancing...”

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Reactive

Adaptive

Generative

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The Systems Perspective

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Dynamics

• Define problems in terms of graphs over time.• Graph important variables• Graph historical data• Graph anticipated dynamics• Graph preferred dynamics

• Use these to focus systems thinking and modeling

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Unemployment (%)

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New York City Population, 1900-2000

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Unemployment & Welfarein Dutchess County, NY

Unemployment

Welfare roll

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Per Capita Residential Energy Use(USA Today 3/23/09, citing Census Bureau and U.S. Energy Information Administration)

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Here’s where we went wrong...

Strive for Insights

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Reactive

Adaptive

Generative

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The Systems Perspective

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• Accumulations (populations, resources…)• Causal structure: “feedback” loops• Delays• Perceptions (a kind of accumulation)• Pressures• Affects, emotions, (ir)rationalities• Policies governing decisions

Systems Structure

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Causal Loop Diagrams

• Causal mapping is a powerful tool for representing structure in complex systems.

• Arrows indicate causal influence.

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Polarities of Causal Links

• Positive and negative signs show the direction of causality:

– +

+ –

+–

+ ... “direct” relation– …“inverse” relation

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Definitions of Link Polarities

All words phrases are expressed as quantities that have a clear sense of increase or decrease. No verbs — the action is in the arrows.

A adds to B, or∆A leads to ∆B in the same direction

C C subtractssubtracts from D, or from D, or∆∆C leads to ∆D in the C leads to ∆D in the oppositeopposite directiondirection

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Simple test for link polarity

An increase in A makes B higher than it would have been without the change.

An increase in C makes D lower than it would have been without the change.

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Examples

“Ceteris paribus”... All other influences held constant as we assign polarities.

Emigration Emigration subtractssubtracts from from population: An increase in population: An increase in emigration means less (a emigration means less (a decrease means more) than wdecrease means more) than wee’’d have without the changed have without the change

More lawyers mean More lawyers mean moremore litigation; fewer lawyers, litigation; fewer lawyers, less litigationless litigation

+

–

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Exercises

d

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Feedback Loops

A feedback loop exists when decisions change the state of the system, changing the conditions and information that influence future decisions.

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The Joy of Feedback

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The Joy of Feedback

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No — it’s more like the life cycle of the famous scientist

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Examples of Feedback Loops

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Two kinds of feedback loops

• Reinforcing loops • Growth producing• Destabilizing• Accelerating• Positive: an even number of –’s

• Symbolized by

• Balancing loops• Counteracting• Goal seeking• Stabilizing• Negative: an odd number of –’s

• Symbolized by

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Examples of Reinforcing Loops

+

+

+ +

+

++

––

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Rockefeller College of Public Affairs and PolicyRockefeller College of Public Affairs and PolicyUniversity at AlbanyUniversity at Albany 26

Isolate and Identify Link Polarity

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Isolate and Identify Link Polarity(Always trace an Increase)

+

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+

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–

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–

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+

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Completed Loop(Now tell the story)

+

– –

++

(R)

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Typical Reinforcing Loop Behaviors20,000

15,000

10,000

5,000

00 25 50 75 100

10,000

9,000

8,000

7,000

6,0000 25 50 75 100

Population and Births Loop

Businesses and Taxes Loop

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World Population (billions)

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6

4

2

01500 1600 1700 1800 1900 2000

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Self-reinforcing processes in world population growth

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Reinforcing Feedback in the Newspaper

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GarfieldGarfield’’s s happinesshappiness

JonJon’’s s suspicionsuspicion

(R)

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Examples of Balancing or Counteracting Loops

+

–+

+–

-+

+

–

+

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Typical Counteracting Loop Behaviors20

15

10

5

00 10 20 30 40

Filling a Glass

10,000

7,500

5,000

2,500

00 25 50 75 100

Population and emigration

•0 •7.5 •15 •22.5 •30

Predator-prey interactions

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Tips for Determining Link and Loop Polarities

• For each link, determine the effect of an increase in the variable at the tail of the arrow:• If the variable at the head increases, assign a plus.• If the variable at the head decreases, assign a minus.

• For each loop, count the number of negative signs:• An even number of negative links is a reinforcing (R) loop.• An odd number of negative links is a balancing (B) loop.

• Most important: For each loop, tell a self-reinforcing or balancing/counteracting story, and check that the story matches the loop polarity.

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More Serious Example from the Newspaper:Recall the graph of per capita energy use

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Presentation Dynamics

ClarifyingquestionsAudience

understanding

Clarity ofpresentation

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Presentation Dynamics- Which loop dominates?

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Stocks and Flows

Stocks are accumulations.• Stocks are increased by inflows and decreased by outflows.• When a link means “add” or “subtract” we have a stock-and-

flow structure.• Example: Inventory

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Stock and Flow Diagramming Conventions

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A Stock and Flow Example

Explicit stocks and flows:

The corresponding causal-loop diagram:

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Human Activity, CO2, and Global Temperature

Thought experiment:

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Structure and Dynamics of Terrorist Cells

New recruits

Terrorist group Losses

Terrorist actions

Suppression activities

Zeal

Peripheral support

Funding

Martyrs to the cause

(R)

(R)

(B)

(R)

(R)

(R) (B)

(R)

(R)

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Balancing Loops in Tobacco Prevalence

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Balancing Loops in Tobacco Prevalence

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Loops and Constituencies

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There are a lot …

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Policy Resistance of Complex Systems

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Policy Resistance in Complex Systems

tools for systems thinking and modeling

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