3.11) Delays

The final feature we can add to a system dynamics model is a delay in the connection between variables. This is represented as:

As before, there is a causal link between A and B, but the link is delayed by a set time period. E.g. an increase in A could cause an increase in B two years later. An example of where a delay could be used is where an environmental process is monitored, such as overfishing, but there is a delay between observation and the implementation of policy responses.

We now have the complete set of primitives from which system dynamics models are constructed: positive and negative causal links, feedback loops, stock and flow variables, and delays.