Fishbone Diagram, also known as Cause and Effect diagram or Ishikawa Diagram, is one of the basic 7QC tools. It is a simple yet powerful tool in the Lean/ Six Sigma / Lean Six Sigma / Operational Excellence toolbox. It is commonly known as the fishbone diagram because it resembles the shape of a fish skeleton. The basic concept was first used in the 1920s and was later refined and made popular by Dr. Kaoru Ishikawa in the 1960s.
Fishbone Diagram is used for identifying potential causes that may contribute to a problem, also known as the effect. It is hence a basic but important tool that should be covered in any Root Cause Analysis Training.
Fishbone Diagram is a qualitative tool and is a useful brainstorming technique for identifying possible causes of problems in operational or business processes. It can be used at any stage of a performance excellence project, or on its own to help identify causes of a particular problem. It should be created in a group setting, utilizing the knowledge and experiences of a variety of individuals. It also goes by the name cause-and-effect diagram because the effect is at the head of the fish, and the causes are documented into categories in the middle of the fish.
To create a Fishbone diagram following steps can be taken:
First, we select the effect and identify the potential causes for the issue. Once you select this effect or problem, you place it in a box on the right-hand side of a piece of paper or whiteboard. This will become the head of the fish. Then create the body of the diagram using a horizontal line from the problem toward the left side. Draw six branches leading out of the fish as a skeleton. Every branch is starting from the Fish main bone or a horizontal line, creating an image that looks like the skeleton of a fish.
After making the fish body, we can move to the next step, which is to add the labels for the categories at the top of each of the major branches of the fish. To brainstorm we should six categories. The final step of constructing a fishbone diagram is to brainstorm the potential causes of the problem or effect. There are many methods you can use to complete this step, but the most important requirement is that you do this through a team activity.
To build a fishbone diagram the team members expertise must be utilized as they might include process owners, process supervisors, practitioners or maintenance individuals that bring experience in working within your process. A brainstorming session will help you identify as many potential causes as possible to fill in the body of the diagram. Following are the categories of the Fishbone diagram:
- Our first category is Personnel. This category refers to any specific individual problems we have in operator training or experience.
- Category number two is Materials. How might our materials affect the problem? This usually implies raw materials or equipment materials.
- Measurement is our third category. This refers to any kind of gauge or inspection issues that may come up.
- The fourth category is Method. This category captures any procedures that may be lacking.
- Category five is Machine. These are any issues associated with the machine settings. These can also be issues with the tools used in a process.
- And finally, our sixth category is Environment. This category refers to any inputs caused by nature or outside noise variables in our process.
The advantage of the fishbone diagram is to identify future areas for possible examination. Once your team has identified potential causes, you can move forward in researching and analyzing the causes that are most likely to cause the problem.
Fishbone diagrams provide areas of focus in handling a problem. Every time a team investigates a new problem, they should go through the process of brainstorming possible causes for that problem. The issues that a single individual cannot think of on his own will show up when a team members brainstorm all the reasons and causes.
An added benefit is that you can relate each of these causes back to inputs that are not in control. The fishbone can guide us the process of identifying critical Xs for future statistical analysis and investigation. After completing the fishbone diagram, the team can start the process of narrow-downing the list of potential causes into a list of the probable ones. From there, you can use a variety of statistical tools to analyze and verify your data.
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