Subject: Endogenous Model

Posted by Richard Turnock on 11/24/2011
In Reply To:Endogenous Model Posted by George Richardson on 11/24/2011

Message:

Building a dynamic model is a process of continuous improvement that changes the boundaries of the system in the model. In addition to the great message about modeling, implied in Dr. Forrester's message is a process of changing the boundaries of the system being modeled. Building a model of a dynamic system is a process of continuous improvement. Janice Hansel says she defined the system boundaries too narrowly. However that is exactly what you should do as the first step. You need to build a working model that is simple then expand the boundaries, then test, evaluate and validate, then repeat. You might reach a point where you expand the boundaries and then realize that you can remove some things. Sharing your model can result in improvements to the presentation of the model. Every step of testing and validation improves the model and can result in changing the boundaries of the system. When do you stop? As Dr. Forrester said, "Therefore, the boundary of a model must be defined in such a way that the source of the problem and its alleviation lie within the boundary." That's when you can declare the model "useful".


Richard