Fishbone (Cause and Effect or Ishikawa) Diagram

The fishbone diagram is one of the seven basic quality control tools.

The fishbone diagram is also known as the Ishikawa diagram, cause and effect diagram, fishikawa diagram, and herringbone diagram.

It got the name fishikawa because Japanese professor Kaoru Ishikawa developed it in 1960, a highly regarded expert in quality management, and it looks like a fish skeleton. It is also called a fishbone diagram for the same reason.

This tool helps you to explore the causes that might be producing the problem. It is imperative for you to know the real cause of the problem before you start thinking about any possible solution.

The fishbone diagram gives you a comprehensive list of possible causes to identify the root cause of the problem. The first advantage of this tool is that it provides you with a better understanding of the problem, and you can eliminate the root cause of the problem in one shot rather than solving a part of the problem the first time, then again solve another part, and so on.

The fishbone diagram uses a brainstorming technique to collect the causes and come up with a kind of mind map which shows you all identified causes graphically. Sometimes, it happens that the most apparent cause turns out to be minor and the cause thought to be a minor one was causing the issue. This diagram gives you an opportunity to think more thoroughly about the root cause of the problem, which leads to a healthy resolution.

The fishbone diagram makes you consider all possible causes of a problem instead of focusing on the most obvious one. Here causes are grouped into several categories to identify the correct source of the variation easily.

Categorization of Causes in a Fishbone Diagram

A fishbone diagram can be used in any industry. You only need to customize the category of causes based on your requirements. For every industry there is a different categorization of causes. Some generic categorizations for popular industries are given below.

In the manufacturing industry, you can categorize the factors (causes) by 6Ms:

• Machine
• Method
• Material
• Manpower
• Measurement (Inspection)
• Milieu (Mother Nature – Environment)
• Management
• Maintenance

Toyota populated the first six, and later on, two more “Ms” were added to the list.

If you’re in the marketing industry, you can categorize these factors by 7Ps:

• Product
• Price
• Place
• Promotion
• People
• Positioning
• Packaging

And if you’re in the service industry, you can categorize these factors by 5Ss:

• Surroundings
• Suppliers
• Systems
• Skills
• Safety

A search on the internet can show you many more classifications; however, the above given classifications are more popular than the rest.

How to Draw a Fishbone Diagram

The following are the steps to draw a fishbone, or cause and effect, diagram.

Identify the Effect (Problem)

First of all write down the problem. Many times it happens that the identification of the main problem is not straightforward. In such cases, a short brainstorming session is helpful to point it out.

Draw a rectangle on the right side of a drawing sheet. Write the problem inside this box and draw a straight arrow towards the left side of the box wall from the left side of the paper. This drawing should look like the spine and head of a fish.

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 problem with categorization, use any of the generic headings given above.

For each possible factor draw a line on the fish spine on the graph as shown in the figure, and label each line. The factors added by you are bones of the fish.

Brainstorm Possible Causes

Now for each category, brainstorm the possible causes of the problem. You can also sub-categorize them if needed. While brainstorming, ask yourself questions like “Why does this happen?” Note the answer. Then again ask “Why does this happen?”

You can add these causes horizontally to the fishbone (factors) they belong and label them. You can continue adding sub-branches until you reach a satisfactory end result. Spend as much time as you can because this is a very important process, and the collection of causes should be very comprehensive.

If you observe this technique, you will notice that it resembles the “5-Why” approach, which says “Discovery of the true root cause requires answering the question ‘Why?’ at least five times”.

Analyze the Diagram

Your fishbone or Ishikawa diagram is complete, and you can see all the possible causes of the problem.

Now, you can sit with your team members and investigate further to identify the root cause of the problem and discuss the solution. And once you decide on the solution, implement it and eliminate the problem from your project.

Important Points to be Noted While Developing a Fishbone Diagram

There are some points you should keep in mind while developing a fishbone diagram, such as:

• There should be clarity on the problem for which you are going to draw the diagram.
• 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 becoming too bulky, try to split it into two or three branches.

Benefits of a Fishbone Diagram

There are many benefits of fishbone diagrams. Some of them are as follows:

• It is a visual tool which is very easy to understand and analyze.
• It helps you identify the root cause of the problem.
• It helps you finding bottlenecks in the process.
• It helps you identify ways to improve the process.
• It helps you when team members are fighting and blaming each other for any problem.
• It involves an in-depth discussion of the problem which educates the whole team.
• It prioritizes further analysis and helps you take corrective action.

Limitations/Drawbacks of a Fishbone Diagram

The following are a few limitations or drawbacks of a fishbone diagram:

• A fishbone diagram does not single out the root cause of the problem. Graphically speaking, all causes look equally important.
• Sometimes, the effort is wasted in identifying causes which have little effect on the problem.
• A fishbone diagram is based on opinion rather than evidence. This process involves a democratic way of selecting the cause, i.e., voting down the causes, which may not be an effective way of identifying causes.
• If the discussion is not appropriately controlled, it may deviate from its objective.

The worthiness of a fishbone diagram is dependent on how you develop the diagram. If the participant is less experienced, less involved and not more knowledgeable, your diagram will be neat and clean, and you might not be able to identify the root cause of the problem.

Therefore to develop a sound fishbone or Ishikawa diagram, involve experienced and experts and ask as many “whys” as you can (up to five “whys” is more than enough).

Summary

A fishbone diagram is a vital tool in identifying the root cause of a problem. Although the development of this diagram is a bit time consuming, the benefits are enormous. This tool helps you remove the root cause of the problem and develop an understanding among team members. These days, a cause and effect diagram is used in all industries whether they are manufacturing, production, marketing, project management, etc.

Here is where this blog post on the fishbone diagram ends. If you have something to share, you can do so through the comments section below.