Problem solving 101, Part 3.

Cause and Effect Diagrams were developed by Kauro Ishikawa of Tokyo University in 1943. Cause-and-effect diagrams or fish bone are used to list the many and varied causes that can be attributed to a problem. These diagrams can help identify the reasons why a process is not performing as intended or hoped.
Cause and Effect Diagrams help you to think through causes of a problem thoroughly. Cause and Effect Diagrams are also known as fish bone Diagrams, because a completed diagram can look like the skeleton of a fish.
How to Use the Tool:
Follow these steps to solve a problem with a Cause and Effect Diagram:
Identify the problem:
Write down the exact problem you face in detail. Where appropriate identify who is involved, what the problem is, and when and where it occurs. Write the problem in a box on the left hand side of a large sheet of paper. Draw a line across the paper horizontally from the box. This arrangement, looking like the head and spine of a fish, gives you space to develop ideas.
Work out the major factors involved:
Next identify the factors that may contribute to the problem. Draw lines off the spine for each factor, and label it. These may be people involved with the problem, systems, equipment, materials, external forces, etc. Try to draw out as many possible factors as possible. If you are trying to solve the problem as part of a group, then this may be a good time for some brainstorming. Using the ‘Fish bone’ analogy, the factors you find can be thought of as the bones of the fish.
Identify possible causes:
For each of the factors you considered in stage 2, brainstorm possible causes of the problem that may be related to the factor. Show these as smaller lines coming off the ‘bones’ of the fish. Where a cause is large or complex, then it may be best to break the it down into sub-causes. Show these as lines coming off each cause line.
Analyze your diagram:
By this stage you should have a diagram showing all the possible causes of your problem that you can think of. Depending on the complexity and importance of the problem, you can now investigate the most likely causes further. This may involve setting up investigations, carrying out surveys, etc. These will be designed to test whether your assessments are correct.
Rigorous analysis which overlooks no possible problem source
creates an easy to understand visual representation of the causes, categories of causes, and the problem statement
The simplicity of a fishbone diagram can be both its strength and its weakness. As a weakness, the simplicity of the fishbone diagram may make it difficult to represent the truly interrelated nature of problems and causes in some very complex situations.

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