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Fishbone Diagram
A Problem-Analysis Tool

What is a Fishbone diagram?

Dr. Kaoru Ishikawa, a Japanese quality control statistician, invented the fishbone diagram. Therefore, it may be referred to as the Ishikawa diagram. The fishbone diagram is an analysis tool that provides a systematic way of looking at effects and the causes that create or contribute to those effects. Because of the function of the fishbone diagram, it may be referred to as a cause-and-effect diagram. The design of the diagram looks much like the skeleton of a fish. Therefore, it is often referred to as the fishbone diagram.

Whatever name you choose, remember that the value of the fishbone diagram is to assist teams in categorizing the many potential causes of problems or issues in an orderly way and in identifying root causes.

When should a fishbone diagram be used?

Does the team...

  • Need to study a problem/issue to determine the root cause?
  • Want to study all the possible reasons why a process is beginning to have difficulties, problems, or breakdowns?
  • Need to identify areas for data collection?
  • Want to study why a process is not performing properly or producing the desired results?

How is a fishbone diagram constructed?

Basic Steps:

  1. Draw the fishbone diagram....
  2. List the problem/issue to be studied in the "head of the fish".
  3. Label each ""bone" of the "fish". The major categories typically utilized are:
  • The 4 M’s:
    • Methods, Machines, Materials, Manpower
  • The 4 P’s:
    • Place, Procedure, People, Policies
  • The 4 S’s:
    • Surroundings, Suppliers, Systems, Skills

Note: You may use one of the four categories suggested, combine them in any fashion or make up your own. The categories are to help you organize your ideas.

  1. Use an idea-generating technique (e.g., brainstorming) to identify the factors within each category that may be affecting the problem/issue and/or effect being studied. The team should ask... "What are the machine issues affecting/causing..."

  2. Repeat this procedure with each factor under the category to produce sub-factors. Continue asking, "Why is this happening?" and put additional segments each factor and subsequently under each sub-factor.

  3. Continue until you no longer get useful information as you ask, "Why is that happening?"

  4. Analyze the results of the fishbone after team members agree that an adequate amount of detail has been provided under each major category. Do this by looking for those items that appear in more than one category. These become the 'most likely causes".

  5. For those items identified as the "most likely causes", the team should reach consensus on listing those items in priority order with the first item being the most probable" cause.

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