An ice-breaker model for people new to System Dynamics modelling:
We have provided a variety of resources and links to support you in the development and use of systems thinking and dynamic modelling. However, we also thought an example and a challenge would be helpful. Consider a simple system in which there are referrals and treatment rates, with a waiting list holding people until there is capacity to treat:
In a System Dynamics model you control the numbers waiting by varying the inflow or outflow rates – just as you would control water in a bathtub through the taps and the plug-hole. In a simple model created to illustrate the dynamic nature of the ‘system’ above we have simulated two feedback elements arising from an increase in the number of people waiting following a temporary reduction in treatment capacity:
- An increase in waiting time can feedback to reduce referral rates as GPs adopt more of a wait and see approach – this is a classic balancing loop.
- An increase in people waiting which increases the risk of urgent treatment, which further reduces treatment capacity for people on the waiting list – this is a classic reinforcing loop and can, without any balancing loops, lead to a run-away system.
This simple simulation is provided below. You can explore the structure and dynamic behaviour over time to get a feel for what a System Dynamics model looks like.
We’ve also set a challenge, purely for learning and education purposes. If you have understood how this model works by exploring the storyline and using the different assumptions to obtain model outputs, and you think you can reproduce part of all of it using a spreadsheet we’d like to hear from you. Please e-mail Peter with your findings and perhaps comment on our blog.