The fishbone diagram which is also known as the Ishikawa diagram, cause and effect diagram, can be used to identify the root cause of a problem.
The fishbone diagram which looks like fish skeleton, was developed by Dr. Kaoru in 1943 at the University of Tokyo. Hence the Fishbone Diagram is frequently referred to as an “Ishikawa Diagram”.
This tool gives you an overall list of possible causes to determine the root cause of the problem. By the help of this visual tool, it is easy to understand what causes a problem and how to solve it.
The Fishbone (Cause and Effect or Ishikawa) Diagram is one of the seven basic tools of quality.
7 BASIC QUALITY TOOLS
The 7 basic quality tools are graphing techniques that people commonly use for quality control troubleshooting purposes. They are easy to use and implement.
- Fishbone (Cause and Effect or Ishikawa) Diagram
- Check sheet
- Control charts
- Pareto chart
- Scatter diagram
Categorization of Causes in a Fishbone Diagram
Fishbone diagrams are widely used in industries such as service, manufacturing, marketing etc. There are a few suggested categories are below.
In the service industry, you can categorize the factors (causes) by 4Ps:
In the Manufacturing industry, you can categorize the factors (causes) by 6Ms:
• Mother Nature (Environment)
In the Marketing industry, you can categorize the factors (causes) by 7Ps:
Many classifications can be made for categorization of causes in a fishbone diagram; however, the above are more popular than the others.
How to Create a Fishbone Diagram
The following are the steps to create a fishbone diagram
1. Identify the Problem (Effect)
The problem expression can be written in a box at the mouth of the fish.
2. Agree on the major categories of causes of the problem
The major categories can be written as branches from the main arrow. Major categories often include: Material, Manpower, People etc.
3. Brainstorm all the possible causes
In this step brainstorming can be made by group/team members based on prior experiences. During brainstorming, ask “Why does this happen?” Note the answer. These causes can be written horizontally to the fishbone they belong. Causes can be written in several places if they relate to several categories.
Again ask “Why does this happen?” about each cause. Write sub-causes branching off the cause branches.
Note that the “five-whys” technique is often used in conjunction with the fishbone diagram – keep asking why until you get to the root cause.
4. Analyze the Diagram
Once the fishbone diagram completed, an investigation can be made with team members to identify the root cause of the problem. Solution can be determined and corrective actions can be taken.
Benefits of a Fishbone Diagram
– It is a visual tool which displays the links and relationships among the potential causes and results displayed in the diagram.
– It demonstrates all causes simultaneously.
– It encourages brainstorming about the reasons for a certain result because it captures all the causes.
– It stimulates your team to explore the root cause of a problem.
– It helps to determine the methods to improve the process and take corrective actions.
Limitations/Drawbacks of a Fishbone Diagram
– For a realistic result, a team is needed to make brainstorming.
– In complex situations it is difficult to represent the interrelated nature of problems and causes.
– Sometimes it can be hard to determine the root cause of a problem because of team members bias.
The fishbone diagram is a powerful process improvement which greatly helps to determine the important factors involved in a process. Creating this diagram encourages teamwork and builds trust between departments. It is widely used in all industries as a problem solving tool.