System Dynamics

System dynamics (SD) is an approach to understanding the nonlinear behavior of complex systems over time using stocks, flows, internal feedback loops, and time delays.

System dynamics is a methodology and mathematical modelling technique to frame, understand, and discuss complex issues and problems.

System Dynamics key considerations:

  • System– a group of independent but interrelated elements comprising an integrated whole
  • systems thinking– the process of understanding how system elements interact to produce system behavior.

The systems are characterized by

  • structure – composition of elements
  • behavior – involved inputs, processes and outputs of material, energy and/or information
  • interconnections – structural and functional relations between elements
  • emerging properties-system properties that do not appear in individual elements (e.g. car individual parts cannot move by themselves)

Emergent properties is that it’s the property of the wholeand only exists as a wholenot a property of the component bits. Emerging properties have a fundamental impact on the system performance. Each organization will have unique emergent properties . emergent phenomena are best understood by observing a ‘pattern resulting from the interactions’ among multiple elements in a system including aspects of the environment.

In the System Dynamics methodology, a problem or a system (e.g., ecosystem, political system or mechanical system) is first represented as a Causal Loop Diagram.

Causal Loop1

A causal loop diagram is a simple map of a system with all its constituent components and their interactions. By capturing interactions and consequently the feedback loops (see figure below), a causal loop diagram reveals the structure of a system. By understanding the structure of a system, it becomes possible to ascertain a system’s behavior over a certain time period.

Stock and flow diagrams

Causal loop diagrams aid in visualizing a system’s structure and behavior, and analyzing the system qualitatively over time. To perform a more detailed quantitative analysis, a causal loop diagram is transformed to a stock and flow diagram. A stock and flow model helps in studying and analyzing the system in a quantitative way; such models are usually built and simulated using computer software.

stock and flow

A stock is the term for any entity that accumulates or depletes over time. A flow is the rate of change in a stock.