Systems Dynamics: Looping the Loop

A simplified idea of Systems Thinking is that there are consequences to every action; some predicted, and some unexpected. In Systems Dynamics this reaction is known as feedback.

A potted history of Systems Dynamics

System dynamics was created during the mid-1950s by Professor Jay Forrester of the Massachusetts Institute of Technology. In 1956, Forrester accepted a professorship in the newly formed MIT Sloan School of Management. His initial goal was to determine how his background in science and engineering could be brought to bear, in some useful way, on the core issues that determine the success or failure of corporations.

From hand simulations (or calculations) of the stock-flow-feedback structure of the industrial and corporate structures, Forrester was able to demonstrate how the instability of employment in a firm was due to the internal structure of the firm. These hand simulations were the start of the field of system dynamics.

Since this time, SD has gone continued to develop and refine through students of Forresters original principles; such as Donella Meadows and Peter Senge.

Reinforcing Loops (R)

A Reinforcing link indicates a situation where an increase in one variable, leads to an increase in another variable, On a diagram this is notated by the inclusion of a + sign on the linking arrow,

A Reinforcing loop (amplification) indicates a self perpetuating trend. A positive feedback loop demonstrates an acceleration of growth, a negative feedback loop indicates the opposite – an accelerated decline or reduction.

It is possible to spot a reinforcing loop because the outcome of the loop will include either zero or an even number of negative links (-).

Balancing Loops (B)

A Balancing loop operates whenever there is a goal-oriented behavior – it acts like a self-correction force.

  • If the goal is to be not moving, then balancing feedback will act the way the brakes in a car do.
  • If the goal is to be moving at hundred kilometers per hour, then balancing feedback will cause you to accelerate to hundred but no faster.

What makes balancing processes so difficult in management is that the goals are often implicit, and no one recognizes that the balancing process exists at all – this is frequently down to  corporate culture (‘something we have always done.’). Identifying these balancing processes is crucial for system dynamics modeling. 

It is possible to spot a balancing loop because the outcome of the loop will include a odd number of negative links (-).

A few tips for drawing feedback loops:

  • + indicates increase creates increase, or decrease creates decrease
  • – indicates increase creates decrease, or decrease creates increase
  • Use curved lines: it is easier to ‘see’ a loop if it looks like a loop. Rectangles are more difficult to ‘see.’
  • Minimise crossed lines; this may mean you will need to draw and redraw a diagram to find the best layout.
  • Keep it clean and uncluttered with extra stuff. It will just distract the message,
  • I use a notebook / whiteboard to draw out (and rub out) feedback loops before transferring it to paper – it is unlikely to be right first time around.

I found the following video online which uses an unexpected topic – Love – to describe some of the common Systems themes. its worth a watch to help visualise the themes:

2 thoughts on “Systems Dynamics: Looping the Loop

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