In chapter 9, we ran "The outsourcing model" in Excel using If analysis. is also descriptive in that it simply allows you to evaluate the cost impact of different (_ _). Note that ) is an uncontrollable variable we can vary to evaluate the costs of the decision alternatives. The model itself does not include any decision variables. Descriptive models are used to explain the behavior of systems, to predict future events as inputs to planning processes, and to assist decision makers in making decisions. \