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What is an Interrelationship Diagram?

Quality Glossary Definition: Interrelationship diagram

Also called: interrelationship diagraph, relations diagram or digraph, network diagram

Variation: matrix diagram

An interrelationship diagram is defined as a new management planning tool that depicts the relationship among factors in a complex situation. The interrelationship diagram shows cause-and-effect relationships. Its main purpose is to help identify relationships that are not easily recognizable.

An interrelationship diagram borders on being a tool for root cause identification, but it is mainly used to identify logical relationships in a complex and confusing problem situation. In such cases, the strength of an interrelationship diagram is its ability to visualize such relationships. The process of creating an interrelationship diagram can help groups analyze the natural links between different aspects of a complex situation.

When to Use an Interrelationship Diagram

  • When trying to understand links between ideas or cause-and-effect relationships, such as when trying to identify an area of greatest impact for improvement
  • When a complex issue is being analyzed for causes
  • When a complex solution is being implemented
  • After generating an affinity diagram, fishbone diagram, or tree diagram to more completely explore the relations of ideas
  • In root cause analysis, particularly for:
    • Understanding how different aspects of the problem are connected
    • Seeing relationships between the problem and its possible causes that can be further analyzed

Interrelationship Diagram Basic Procedure

Materials needed: Sticky notes or cards, large paper surface (newsprint or two flipchart pages taped together), marking pens, and tape.

  1. Write a statement defining the issue that the interrelationship diagram will explore. Write it on a card or sticky note and place it at the top of the work surface.
  2. Brainstorm ideas about the issue and write them on cards or notes. If another tool has preceded this one, take the ideas from the affinity diagram, the most detailed row of the tree diagram, or the final branches on the fishbone diagram. If helpful, use these ideas as starting points and brainstorm additional ideas.
  3. Place one idea at a time on the work surface and ask, "Is this idea related to any others?" Place ideas that are related near the first. Leave space between cards to allow for drawing arrows later. Repeat until all cards are on the work surface.
  4. For each idea, ask, "Does this idea cause or influence any other idea?" Draw arrows from each idea to the ones it causes or influences. Repeat the question for every idea.
  5. Analyze the diagram:
    • Count the arrows in and out for each idea. Write the counts at the bottom of each box. The ones with the most arrows are the key ideas.
    • Note which ideas have primarily outgoing (from) arrows. These are basic causes.
    • Note which ideas have primarily incoming (to) arrows. These are final effects that also may be critical to address.

Remember, the number of arrows is only an indicator, not an absolute rule. Be sure to check whether ideas with fewer arrows also are key ideas. Draw bold lines around the key ideas.

Create an Interrelationship Diagram for Root Cause Analysis

  1. Determine the factors to be analyzed for possible relationships and label these using brief and succinct definitions.
  2. Plot the factors on an empty chart on a whiteboard, preferably in a roughly circular shape.
  3. Assess what impacts each factor and which factors are impacted by it, and illustrate the relationships using arrows.
  4. After all relationships have been assessed, count the number of arrows pointing into and away from each factor and denote this information on the diagram.
  5. Depending on the number of arrows pointing in each direction for a factor, it can play one of two roles: driver (more arrows away from than into), or indicator (more arrows into than away from).
  6. When continuing the root cause analysis, the drivers form the starting point.

Tools for Creating an Interrelationship Diagram

Interrelationship Diagram Example #1

A computer support group is planning a major project: replacing the mainframe computer. The group drew an interrelationship diagram (see Figure 1) to sort out a confusing set of elements involved in this project.

Relations Diagram Example
Figure 1: Interrelationship Diagram

"Computer replacement project" is the card identifying the issue. The ideas that were brainstormed were a mixture of action steps, problems, desired results, and less-desirable effects to be handled. All these ideas went onto the diagram together. As the questions were asked about relationships and causes, the mixture of ideas began to sort itself out.

After all the arrows were drawn, key issues became clear. They are outlined with bold lines.

  • "New software" has one arrow in and six arrows out. "Install new mainframe" has one arrow in and four out. Both ideas are basic causes.
  • "Service interruptions" and "increased processing cost" both have three arrows in, and the group identified them as key effects to avoid.

Interrelationship Diagram Example #2

A small hospital was concerned about the productivity of its doctors because they were the most expensive employees and critical for the treatment of the patients. Having taken numerous steps toward ensuring high productivity, hospital management was baffled when productivity steadily declined month after month.

Since this development was unexplainable, management sought to gain insight into causes and effects among the different factors at play. They decided to create an interrelationship diagram and include the following factors in the analysis:

  • The number of scheduled appointments per doctor
  • The number of emergency appointments per doctor
  • Administrative workload per doctor
  • The number of changes in scheduled appointments
  • Equipment quality and reliability
  • Nurse availability
  • Availability of other support functions
  • The doctors’ pay levels

When the interrelationship diagram had been completed (Figure 2), attention shifted from improving the doctors’ work situation to ensuring the availability of nurses, other support functions, and operational equipment.

Relations Diagram
Figure 2: Interrelationship Diagram

Adapted from The Quality Toolbox, Second Edition and Root Cause Analysis: Simplified Tools and Techniques, ASQ Quality Press.

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