Why delays exist in system dynamics given the fact that nothing is standstill in the system dynamics world? When there is a delay between training and its impact on productivity it is not the case that nothing is happening in the duration of 'delay'; nothing is standstill during that period. Delay is only for the purpose of modeling.
Cause and Effect are separated in time and hence the delay. However, this holds for every causal link. In that sense every causal link will have delay. The question is what are the considerations we need to take while modeling delays in system dynamics?
Thanks Monica for attempting this question. Would it be not interesting to model what happens during the delay?
A model of reality is not just a single cause and effect path with a potential delay in it. There are always a lot of parallel paths with additional dynamic properties around, which describe other processes happening in parallel and simultaneously during a delay in one single path. Its all a question of your modelling your reality. Signal and System Theory does only, what you model and will provide you with simulation results accordingly, wright or wrong: garbage in, garbage out!
There is extensive work on modelling using delays, mostly to my knowledge in the qualitative use of SD, but one of the hottest research topics is how to diagnose structural instability and the delay elements play a part in this.
For instance, there is an element of delay between end of training and increase in productivitity to measure training effectiveness. It is not always clear what happens during this interim period we call 'delay'. In case of a long pipe bringing water to the tank dynamics of water in the pipe before reaching the tank can be modeled and what happens during the interim period is visible.