Cause and Effect Diagram, Fishbone Diagram or Ishikawa diagram, is an widely used tool to help users to find the roots causes of the problems they are investigating. The approach combines brainstorming and a concept map. The process has four major steps: identifying the problem; working out the major factors involved; identifying possible causes and analyzing the cause and effect diagram, which are used to resolve numerous problems including risk management in production and services. (I diagram mainly represents a model of suggestive presentation for the correlations between an event (effect) and its multiple happening causes. The structure provided by the diagram helps team members think in a very systematic way. Some of the benefits of constructing a fishbone diagram are that it helps determine the root causes of a problem or quality characteristic using a structured approach, encourages group participation and utilizes group knowledge of the process, identifies areas where data should be collected for further study (Basic tools for process improvement).
The design of the diagram looks much like the skeleton of a fish. The representation can be simple, through bevel line segments which lean on a horizontal axis, suggesting the distribution of the multiple causes and sub-causes which produce them, but it can also be completed with qualitative and quantitative appreciations, with names and coding of the risks which characterizes the causes and sub-causes, with elements which show their succession, but also with other different ways for risk treatment. The diagram can also be used to determine the risks of the causes and sub-causes of the effect, but also of its global risk.
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The C-and-E diagram has nearly unlimited application in research, manufacturing, marketing, office operations and so forth. One of its strongest assets is the participation and contribution of everyone involved in the brainstorming process. Solutions are developed to correct the causes and improve the process. Criteria for judging the possible solutions include cost, feasibility, resistance to change, consequences, training and so forth. Once the solutions have been agreed to by the team, testing and implementation follow. Diagrams are posted in key locations to stimulate continued reference as similar or new problems arise. The diagrams are revised as solutions are found and improvements are made.
The Fishbone Diagram can created by following the steps described below:
1. Identification of the problem
2. Formalization of the problem
3. Identification of main and secondary causes
4. Establishment of priority criteria
5. Completion of cause and effect diagram
6. Analysis of the diagram
7. Acceptance of the diagram
It should be emphasized that root cause diagrams created in brainstorming sessions so active contribution of all project members especially people who are engaged with the particular process very often are essential for correct addressing of the root causes.
For one particular problem, there can be more than one cause. For each of these causes why questions should be asked to reach the root causes of the problem. Theoretically, it is suggested that the root cause of the problem should be found asking why question up to five times. There also needs to be an agreement for each identified causes of the problem within the members of the team.