Cause and Effect Diagram | Fishbone Diagram (Kaoru Ishikawa)

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What is a Cause and Effect Diagram? Description

The Cause and Effect Diagram (Fishbone Diagram) from Japanese quality control statistician Kaoru Ishikawa is a graphical technique that can be used in teams to identify and arrange the causes of an event or problem or outcome. It graphically illustrates the hierarchical relationship between the causes according to their level of importance or detail and a given outcome. Also called: Ishikawa Diagram.
 

Origin of the Fishbone Diagram. History

The Fishbone Diagram was invented by Professor Kaoru Ishikawa of Tokyo University, a highly regarded Japanese expert in quality management. He first used it in 1943 to help explain to a group of engineers at Kawasaki Steel Works how a complex set of factors could be related to help understand a problem.

Usage of the Cause and Effect Diagram | Fishbone Diagram. Applications

• Concentrating on a complex problem in a team effort. Compare: 8D Problem Solving
• Identify all causes and the the root causes for a specific effect, problem, or condition.
• Analyze and relate some of the interactions among the factors affecting a particular process or effect.
• Enable corrective action.

Steps in creating an Ishikawa Diagram. Process

1. Explain the purpose of the meeting. Then identify, and clearly state, and agree on the problem or effect to be analyzed.

2. Position a whiteboard or flipchart so that everyone can see it. Draw a box containing the problem or effect on the right side of the diagram with a horizontal spine.

3. Conduct a Brainstorming session. As a first draft, for the main branches you can use the following Categories:
   • Services industry: the 8 Ps: People, Product/Service, Price, Promotion, Policies, Processes, Procedures, Place/Plant/Technology.
   • Manufacturing: the 6 Ms: Manpower, Methods, Measurements, Machinery, Materials, Mother Nature (environment).
   • Use the above categories by asking for example: What are the People issues affecting/causing the problem?

4. Identify the main causes contributing to the effect being studied. This could be done applying a Pareto Analysis (80/20 rule) or a Root Cause Analysis.

5. These main causes become the labels for the sub branches of your diagram.

6. For each major sub branch, identify other specific factors which may be the causes of the effect. Ask: Why is this cause happening?
7. Identify increasingly more detailed levels of causes and continue organizing them under related causes or categories.
8. Analyze the diagram.
9. Act on the diagram. Remove the causes of the problem. Generic systematic approaches for this are the Deming Cycle or RACI.

Strengths the Cause and Effect Diagram. Benefits

• Helps to find and consider all possible causes of the problem, rather than just the ones that are most obvious.
• Helps to determine the root causes of a problem or quality characteristic in a structured way.
• Encourages group participation and utilizes group knowledge of the process.
• Helps to focus on the causes of the issue without resorting to complaints and irrelevant discussion.
• Uses an orderly, easy-to-read format to diagram cause-and-effect relationships.
• Increases knowledge of the process by helping everyone to learn more about the factors at work and how they relate.
• Identifies areas for further study where there is a lack of sufficient information.

Limitations of the Ishikawa Diagram. Disadvantages

• Not particularly useful for extremely complex problems, where many causes and many problems are interrelated.

Assumptions of the Fishbone Diagram. Conditions

• A problem is composed of a limited number of causes, which are in turn also composed of sub causes.
• Distinguishing these causes and sub causes is a useful first step to deal with the problem.

Book: Kaoru Ishikawa - Guide to Quality Control -

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Compare with the Cause and Effect Diagram: 8D Problem Solving  |  Root Cause Analysis  |  Theory of Constraints  |  Dialectical Inquiry  |  Mind Mapping  |  Pyramid Principle  |  Delphi Method  |  Analogical Strategic Reasoning  |  Action Learning  |  Brainstorming  |  Six Thinking Hats  |  Kepner-Tregoe Matrix  |  RACI  |  Gantt Chart

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