The fishbone diagram is one of the seven basic quality control tools. Though all these tools have their importance, the fishbone diagram is distinct.
In Six Sigma, you use it in the “Analyze” phase of DMAIC. DMAIC stands for define, measure, analyze, improve, and control.
This diagram got the name Ishikawa because Japanese professor Kaoru Ishikawa developed it in 1960. Mr. Ishikawa was a famous expert in quality management.
Project managers use this diagram during quality management. The fishbone diagram has many names, such as Ishikawa diagram, Fishikawa diagram, Herringbone diagram, and the cause and effect diagram.
It is difficult to find another tool with as many names.
This diagram looks like a fish skeleton; the head is the problem and the causes are connected with the spine; therefore, many experts call it a fishbone or herringbone diagram, or Fishikawa, for the same reason.
Since this tool helps you find the cause of the problem, it got the name cause and effect diagram.
What is a Fishbone Diagram?
If you have any problem with your process or product, you should know the cause before thinking about any solution.
A fishbone diagram helps you to find the cause of the problem. It gives you a comprehensive list of causes to find the root of the problem.
This tool provides you with a better understanding of the problem and makes sure you don’t just partially solve a problem.
The fishbone diagram uses a brainstorming technique to collect the causes and show them graphically. Sometimes, the most apparent cause turns out to be minor, and the one that was thought to be minor is causing the issue. This diagram gives you an opportunity to think thoroughly about the root cause, which leads to a healthy and long-lasting resolution.
The fishbone diagram considers all possible causes of a problem, instead of focusing on the obvious one, and groups causes to identify the source of the variation.
Categorization of Causes in a Fishbone Diagram
Every industry uses fishbone diagrams; however, they may have a different categorization of causes. You only need to customize the category as per your requirements.
A few generic categorizations for popular industries are given below.
You can categorize the factors (causes) by the 6 Ms:
- Measurement (Inspection)
- Milieu (Mother Nature–Environment)
Toyota populated the first six, and later on, two more “Ms” were added to the list.
You can categorize these factors by the 7 Ps:
You can categorize these factors by the 5 Ss:
How to Draw a Fishbone Diagram
The following are the steps to draw a cause and effect diagram:
- Identify the Problem
- Identify and Categorize Causes
- Brainstorm Possible Causes
- Analyze the Diagram
Identify the Problem (Effect)
First, write down the problem. Often, identifying the main problem is not straightforward. In such cases, a short brainstorming session is helpful.
Draw a diagram as shown below. Write the problem inside a box and draw an arrow towards the box from the left side of the paper. You will see that it looks similar to the spine and head of a fish. The head of the fish is the problem.
Identify and Categorize Causes
In this step, you will identify all the main factors of the problem and categorize them, for example, Category-I, Category-II, etc. If you are having a problem with categorization, use any of the generic headings given above.
For each factor draw a line on the fish’s spine on the graph as shown in the figure and label each. The factors added by you are the bones of the fish.
Brainstorm Possible Causes
For each category, brainstorm the possible causes of the problem. You can sub-categorize them if needed. While brainstorming, ask yourself questions like “Why does this happen?” Note the answer. Then ask again, “Why does this happen?”
You can add these causes horizontally to the fishbone (factors) and label them. You can continue adding sub-branches until you reach a satisfactory result. This is an important step; you should spend a considerable amount of time here. The collection of causes should be comprehensive.
This technique resembles the “5-Why” approach, which says the discovery of the true root cause requires answering “Why?” at least five times.
Analyze the Diagram
Your fishbone diagram is complete, and you can see all the possible causes of the problem.
Now, you can further investigate with your team to find the root cause and the solution.
Important Points While Developing a Fishbone Diagram
You should keep the following points in mind while developing a fishbone diagram:
- You should have a clear understanding of the problem.
- Team members should be experienced and involved with the problem.
- The discussion should be focused and moderated by the project manager.
- Think of all possible causes for each factor and add them to the bone.
- If any bone is bulky, try to split it into two or three branches.
Benefits of a Fishbone Diagram
A fishbone diagram has many benefits, and a few of them are:
- Being a visual tool, it is easy to understand and analyze.
- It helps you identify the root cause of the problem.
- It helps you locate bottlenecks in the process.
- It helps you find ways to improve the process.
- It involves an in-depth discussion of the problem, which educates the team.
- It prioritizes further analysis and helps you take corrective action.
Limitations of a Fishbone Diagram
The following are a few limitations of a fishbone diagram:
- A fishbone diagram does not single out the root cause of the problem because all causes look equally important.
- Effort can be wasted on identifying causes that have little effect on the problem.
- A fishbone diagram is based on opinion rather than evidence.
- This process democratically selects the cause, which is not an effective process.
- If the discussion is not controlled, you could get incorrect results.
The worthiness of a fishbone diagram depends on the expertise of team members. If they are not experienced and skilled, finding the root cause of the problem will be difficult.
Therefore, involve experienced experts and ask many “whys”. Up to five “whys” is enough.
A fishbone diagram is a vital tool in identifying the root cause of a problem. Although using it is time-consuming, the benefits are enormous. This tool helps you remove the root cause of the problem and develop an understanding among team members. You use the fishbone diagram with a critical problem because you cannot spend much time on every small issue.
Do you use fishbone diagrams in your project? What categorizations have you used and what was your experience? Please share your experiences in the comments sections.