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Spring, 2018 Esc 59M, Boğaziçi University
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– Problem articulation • Theme selection • Key variables • Time horizon • Dynamic problem identification (reference modes)
– Formulation of dynamic hypothesis • Initial hypothesis generation • Endogenous focus • Mapping
– Formulation of a simulation model • Specification of structure • Estimation of parameters
– Validation • Validation of the structure • Validation of the behavior
– Policy design and evaluation • Scenario specification • Policy design • What if analysis • Sensitivity analysis • Interactions of policies
– Implementation Issues, deliberative processes
Overview of the System Dynamics method
Spring, 2018 Esc 59M, Boğaziçi University
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Problem articulation (identification)
• Theme selection • Key variables • Time horizon • Dynamic problem identification (reference
modes)
Examples: A model designed to understand how the business cycles can be stabilized. Addresses only a set of limited issues. Problem: instability; cycles. Purpose: to stabilize. A model designed to explore policies to slow fuel use and mitigate global warming. Problem: increasing fosil fuel consumption. Purpose: to design policies to slow down fosil fuel consumption A model of the national economy: ill defined!
Spring, 2018 Esc 59M, Boğaziçi University
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Illustrating reference modes
US oil production, consumption, imports and price over a 10 year time horizon
Spring, 2018 Esc 59M, Boğaziçi University
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Illustrating reference modes
US oil production, consumption, imports and price over a 130 year time horizon (Davidsen 1988)
Spring, 2018 Esc 59M, Boğaziçi University
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More reference modes
Emissions
0
1000
2000
3000
4000
5000
6000
7000
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990
Global carbon emissions – million tonnes (http://cdiac.esd.ornl.gov/trends/emis/tre_glob.htm)
A multiple reference mode: North sea fish stocks – 1000 tonnes (UNEP – global environmental outlook 2000)
Spring, 2018 Esc 59M, Boğaziçi University
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• Work on a theme that you (and your
potential audience) are interested in
• Model a problem. Not a system.
• Be skeptic about the time horizon of your reference mode. Choose a time horizon several times as long as the longest time delays in the system.
• Try to choose ”feedback” (closed loop) problems.
Useful principles in problem identification
Spring, 2018 Esc 59M, Boğaziçi University
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Formulating a dynamic hypothesis
– Initial hypothesis generation – Focus on endogenous factors (arising
from within): Boundary selection – Mapping (causal loop diagrams etc.)
Spring, 2018 Esc 59M, Boğaziçi University
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Focus in endogenous factors
traffic volume
route capacity
average travelingtime
drivingattractiveness
number of trips
length of trips
car ownership
pressure toconstruct
route construction
route capacity
average travelingtime
number of trips
length of trips
car ownership
Spring, 2018 Esc 59M, Boğaziçi University
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Examples for mapping
Spring, 2018 Esc 59M, Boğaziçi University
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Examples for mapping
Spring, 2018 Esc 59M, Boğaziçi University
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Overview of the modeling process
• Formulation of a simulation model – Specification of structure – Assessment - estimation of parameters
• Validation (testing the model)
– Validation of the structure – Validation of the behavior
parameter estimation
experimental design
• Policy optimization
• Policy design and evaluation – Scenario specification – Policy design – Sensitivity analysis – Interactions of policies
Spring, 2018 Esc 59M, Boğaziçi University
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System dynamics and the scientific method:
• Modeling is iterative
1. Problem Articulation(Boundary Selection)
3. Formulation4. Testing
5. PolicyFormulation& Evaluation
2. DynamicHypothesis
Results of any step can yield insights that lead to revisions in any earlier step