Ensuring model accuracy and validity is a critical task and there are a number of procedures that may be carried out in order to help obtain confidence in your model results. These confidence-building activities include:
· Historical Tests: Comparing the results of the model to known historical values.
· Extreme Value Tests: Testing how the model behaves when extreme values are inputted into it. Does the model behave as one would expect or does it exhibit wild behavior?
· Submodel Tests: For large models it is sometimes possible to isolate one portion of the model and compare it to some other more detailed model designed for analyzing that specific feature.
In addition to these methods, Insight Maker includes a rich suite of features designed for documenting the assumptions that your model is based on and ensuring that these assumptions are not violated during model simulation.
For instance, imagine you are designing a model simulating an ecosystem. As part of this complex model, you may have a stock representing the quantity of water in a lake. When designing your model, you know that the value of the lake stock should never become negative. If it does, there is clearly something wrong with your results and you should analyze the model to see what is causing this error. Unfortunately, though this constraint is fresh in your mind when you are focusing on the lake, it is very easy to forget about it when you focus on a different item. When you move on to another part of your model you might inadvertently make a change to your model that violates the assumption about the lake. Possibly you add another flow that results in the lake stock becoming negative and, since your focus distracted, you do not realize this mistake until much later.
In order to prevent mistake like these, Insight Maker includes a set of tools for documenting and enforcing your model’s assumptions as you develop them. These tools include: Unit Checking and Constraint Checking. All of these tools can be accessed by clicking the model verification button that appears in the configuration pane when you select a stock, flow, converter, or parameter within your model. Once you have defined verification checks for a primitive, a checkmark will appear on the primitive’s verification button letting you know that primitive will be validated during the simulation.