System Dynamics

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System Dynamics “An approach to understanding the behaviour of complex systems over time. It deals with internal feedback loops and time delays that affect the behaviour of the entire system. What makes using system dynamics different from other approaches to studying complex systems is the use of feedback loops and stocks and flows. These elements help describe how even seemingly simple systems display baffling nonlinearity.” (Wikipedia, 2014) System Science(s): Study of systems Linear Causality B A C Cause Effect Circular Causality A Feedback: shows how actions can reinforce (positive feedback) or counteract (balance through negative feedback) each other Variables are organized in a circle C B or loop of cause-effect relationship called a “feedback process” Feedback Processes Reinforcing (R) or Balancing (B) or Amplifying Stabilizing • Operates when there is a • Cause dramatic growth or goal oriented behavior collapse (implicit or explicit) • Amplifies change • Keep things under control • Snowballing effect • Limit dramatic growth • Make something greater or less • Ensure that systems fulfills • Accelerating growth or decline its purpose • “Vicious cycles”, “self fulfilling • Seeks equilibrium and stability prophecies”, “Virtuous cycles” • Self correction to keep goal or target Reinforcing Feedback Balancing Feedback Delay = interruption between actions and their consequences Causal Loop Diagrams (CLDs) http://www.nytimes.com/2010/04/27/world/27powerpoint.html?_r=0 Stock and Flow Diagrams Flow and Stock Stock: Anything that accumulate and can be measured at one point in time (water in bathtub or behind a dam, population, wood in the forest, etc.) Flow: Anything that changes over time (number of births, inflation rate, etc.). Inflows and outflows Stock and flow obey laws of conservation and accumulation Using iThink or Stella Trademark of Isee systems (www.iseesystems.com) Introduction to Systems Thinking by Richmond (2004 a,b). Other SD software include Vensim and Powersim. System Dynamics Modeling and Archetypes Modeling Mixed Modeling Methods Systems Archetypes (archetypos = first of its kind) Limits to growth Fixes that backfire Shifting the burden Eroding goals Escalation Success to the successful Tragedy of the commons Growth and under-investment Balancing process with delay .

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