4.4 Diagrams for further analysis and quantitative model building
To gain further understanding of the connectivity in a situation, a multiple cause diagram can be converted into a sign graph by indicating whether the cause has a positive effect or a negative effect by adding the respective signs. Not all multiple cause diagrams lend themselves to this treatment as you need much greater knowledge of the situation to be able to be sure about the causal chains in a situation and the effects they are likely to have. Sign graphs are particularly useful for establishing the variables and relationships needed for a quantitative mathematical model.
Process engineers have long used diagrams to describe processes. Among these are input-output (or ‘black box’) diagrams and flow diagrams, in which linked ‘inputs’ and ‘outputs’ are described. These are sometimes split into flow-block diagrams describing flows between components and flow-process diagrams describing flows between processes. Others include decision sequence diagrams, in which ‘decisions’ lead to ‘actions’ which lead to new ‘decisions’, and algorithms (or flow charts) in which the type of decision and the impact of alternative outcomes to a decision are set out diagramatically. These all tend to be more suited to situations where the connectivity is relatively clear. Algorithms or flow charts are also invaluable when trying to convert a mathematical model into the steps that can then be translated into computer software code.