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:
- Draw the fishbone diagram....
- List the problem/issue to be studied in the "head of
the fish".
- 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:
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.
-
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..."
-
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.
-
Continue until you no longer get useful information as
you ask, "Why is that happening?"
-
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".
-
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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