The Fishbone Diagram, also known as the Cause and Effect Diagram or Ishikawa Diagram, is a graphical tool used to identify and explore on a single chart, in increasing detail, the possible causes which lead to a given effect.
They are a structured framework that takes advantage of the collective knowledge of a team to identify the main causes of the effect under study.
The ultimate aim is to work down, or drill-down, through the causes to identify basic root-causes of a problem.
The structure provided by the diagram helps team members think in a very systematic way. Some of the benefits are that it:
Constructing a Fishbone Diagram (Cause and Effect Diagram) can help a team when it needs to:
When you develop a Fishbone Diagram (Cause and Effect Diagram), you are constructing a structured, pictorial display of a list of causes organized to show their relationship to a specific effect.
The picture below shows the basic layout of diagram. Notice that the diagram has a cause side and an effect side. The steps for constructing and analyzing a Cause and Effect Diagram are outlined below.
Fishbone Diagram showing major and sub-cause categories.
Reference: The Memory Jogger
A. Major Cause Categories.
B. High level cause.
C. Root cause, i.e. cause of a cause.
D. Secondary root cause, i.e. cause of a root cause.
E. The effect of the causes, i.e. the problem whose causes is being investigated.
The Major Cause Categories are not firmly defined, and can easily vary according to the situation, or the type of problem being studied.
For example, six categories are typically used in manufacturing processes:
Similarly, four are typically used with administrative processes:
Depending on the situation, other categories are possible. Fishbone Diagrams are best prepared in a team setting using Brainstorming techniques, but can also be based on process data if it is available. The same cause should not be used on several exercises.
1. Select the Problem Statement, or Effect, summarized in a few key words, and place it in a box on the right side of the new diagram.
2. Select the Major Cause Categories, according to the specific situation and problem statement, and connect them with a straight line to the “backbone” of the diagram.
3. Place brainstormed or data-driven causes in the appropriate Category.
4. Place Root Causes, against each of the main causes.
5. Continue driving down, identifying further lower-level Root Causes.
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