Cause and Effect Diagram:

The cause and effect diagram is used to explore all the potential or real causes (or inputs) that result in a single effect (or output). Causes are arranged according to their level of importance or detail, resulting in a depiction of relationships and hierarchy of events. This can help in search for the root causes, identify areas where there may be problems, and compare the relative importance of different causes.
Causes in a cause & effect diagram are frequently arranged into four major categories.
• manpower, methods, materials, and machinery (recommended for manufacturing)
• Equipment, policies, procedures, and people (recommended for administration and service).
The cause-and-effect diagram is also called the Ishikawa diagram (after its creator, Kaoru Ishikawa of Japan), or the fishbone diagram (due to its shape).

Steps to use the Cause and Effect Diagram:
1. Identify the problem
Write down the exact problem 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 space to develop ideas.
2. 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.
3. Identify possible cause
For each of the factors that are 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 it down into sub-causes. Show these as lines coming off each cause line.

4. Analyze your diagram
By this stage a diagram should have formed showing all the possible causes of the problem that we can think of. Depending on the complexity and importance of the problem, now investigate the most likely causes further. This may involve setting up investigations, carrying out surveys, etc. These will be designed to test whether the assessments are correct.