The fishbone diagram, cause and effect, or ishikawa diagram is one of the most common quality tools used today. Best known by its resemblance to a fish's body the fishbone diagram is used to show the many possible causes for an effect. The tool is used to help coordinating brainstorming in an effort to discover root causes.
The ishikawa diagram was founded in 1968 by Kaoru Ishikawa. Dr. Ishikawa pioneered a major quality movement while working at Kawasaki. One of the fundamental tools he used on many of his projects was the ishikawa diagram. The tool is still used today by many different industries and has proved its worth on many different levels.
One of the most common mistakes made with the Ishikawa diagram is the belief that there are set categories for each of the branches. Although the 6M fishbone and the 8M fishbone are globally recognized as the standard for manufacturing, transactional processes often utilize a 7P fishbone diagram. Ultimately the categories are based on the team's agreement with possible categories that might be related to the problem that is being analyzed.
The fishbone diagram is commonly paired with the 5 why analysis in order to drill down to the root cause. Here is a general process that you can follow to conduct a root cause analysis.
Step 1 - Clearly define your effect or the problem you are trying to solve. Some examples of the effect maybe quality issues that aren't meeting a standard or a particular process that does not meet the required metrics. This can take a bit of practice as often times the initial problem problem may not be revealed right away.
Step 2 - Once you have clearly defined a problem and gained consensus from any team member who might be involved it is now time to start building the "bones" of our fish. These are the categories that we talked about earlier on. As a reminder the 6M or 8M fish bones are widely accepted in manufacturing, the 7P is commonly used in transnational or marketing situations and the final type of ishikawa diagram is the 5S diagram. Please remember though, no fishbone diagram is set in stone so your team should pick the most appropriate categories for the problem you are trying to solve.
Step 3 - The next step is to begin brainstorming with your team. The brainstorming will be focused on identifying possible causes that are associated with the effect. If a cause is identified and the team agrees on the cause, draw a line on the appropriate categories/bone and label the cause. After it has been placed under the appropriate category it will then be time to start "digging."
Step 4 - Though the 5 why's are not exactly a part of the cause and effect diagram, the two work together quite effectively. Once all the possible causes are in the appropriate category begin asking why. A good practice is to ask the individual that identified the problem why did that happen? Then wait for the answer (at the gemba if possible). Once you have received the answer ask why again until you have reached the "root cause."
There are many different ways of using the fishbone diagram but the 4 steps above should help you get started. Please feel free to send us a message if you run into any trouble using the fishbone diagram, we would love to help. Enjoy.