In the process of building a model, novice modelers often make the mistake of jumping into designing models with detailed information. We also have a problem translating an initial vague understanding of a problem into a concrete model. This is where the influence chart comes into play. An influence chart is a simple diagram that shows what outcome variables the model will generate and how these outputs are calculated from the necessary inputs. Influence charts encourage the modeler to focus on major choices, such as what to include and what to exclude from the model, rather than on details that may be unimportant. The influence chart is not a technical flowchart that must conform perfectly to a rigid set of rules. Some steps to consider when putting together the influence chart are:
- Start with the outcome measure.
- Decompose the outcome measure into a small set of independent variables that determine it directly.
- Take each variable in turn and repeat this process of decomposition.
- Identify input data and decisions as they arise
- Make sure that each variable appears only once in the diagram.
- Highlight special types of elements with consistent symbols.
When highlighting these special elements, use consistent symbols such as squares to maybe show decisions made or octagons to show your objectives, the triangle can be used to show fixed input parameters and you might use the circle to show a variable. The idea here is to be consistent with your symbols.
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