Interrelationship Digraphs

An interrelationship digraph, also called a relations diagram or network diagram, is a tool that depicts relationships among different elements, areas, or processes through a network of boxes and arrows. It is usually used by Six Sigma teams to understand cause-and-effect relationships among different factors of a problem.

Different factors associated with a problem are entered in boxes or written on sticky notes. Factors related to one another are placed close to each other. If any factor causes or influences any other factors, then an arrow is drawn from that factor to those affected factors. At the end of the exercise, the arrows are counted. Generally, boxes with the most arrows leading to them are the major issues. However, this is not a hard-and-fast rule. Sometimes, even key issues may have only a few arrows. Therefore, no issue should be ignored. Issues that have more outgoing arrows are regarded as major causes, whereas issues that have more incoming arrows are regarded as major effects.

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Interrelationship digraphs are used by organizations in different situations for varying purposes.

They are generally used for:

  • Analyzing any kind of relationship, besides cause-and-effect relationships.
  • Analyzing complex issues involving several interrelated issues.
  • Determining areas of improvement that will have the greatest impact on the
  • Analyzing logical relationships.
  • Analyzing problems where causes cannot be organized as hierarchies or matrices.
  • Analyzing a problem that is believed to be caused by another problem.
  • And, developing a better understanding of the relations identified using tools such as affinity diagrams.

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