fishbone, cause and effect, ishikawa diagram

The fishbone diagram is one of the seven basic quality control tools. Though all these tools have their importance, the fishbone diagram is distinct. 

Project managers use this diagram during quality management. The fishbone diagram has many names: the Ishikawa diagram, Fishikawa diagram, Herringbone diagram, and the cause-and-effect diagram.

In Six Sigma, you use it in the “Analyze” phase of DMAIC ( define, measure, analyze, improve, and control). 

This diagram got the name Ishikawa because Professor Kaoru Ishikawa developed it in 1960. Mr. Ishikawa was a famous expert in quality management.

This diagram looks like a fish skeleton; the head is the problem, and the spines are the causes; many experts call it a fishbone, herringbone diagram, or Fishikawa. 

Fishbone Diagram

If you have a problem with your process or product, you should know the cause before thinking about a solution. 

A fishbone diagram gives you a comprehensive list of causes to find the root of the problem. 

This tool provides you with a better understanding and makes sure you don’t just partially solve a problem. 

The fishbone diagram uses a brainstorming technique to collect causes and show them graphically. Sometimes, the most apparent factor turns out to be minor, and the one that was thought to be minor is causing the issue. This diagram allows you 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. It also groups cause to identify the source of the variation.

cause and effect diagram, ishikawa diagram

Categorization of Causes in a Fishbone Diagram

Every industry uses fishbone diagrams; however, they may have a different categorization of causes. You need to customize the category to your requirements. 

A few generic categorizations for popular industries are given below.

Manufacturing Industry

You can categorize the factors (causes) by the 8 Ms:

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

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

Marketing Field

You can categorize these factors by the 7 Ps:

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

Service Industry

You can categorize these factors by the 5 Ss:

  • Surroundings
  • Suppliers
  • Systems
  • Skills
  • Safety

How to Draw a Fishbone Diagram

  1. Identify the Problem
  2. Identify and Categorize Causes
  3. Brainstorm Possible Causes
  4. Analyze the Diagram

Identify the Problem (Effect)

First, write down the problem. When the main problem is not straightforward, a short brainstorming session is often helpful.

fishbone diagram-step-1

Draw a diagram as shown. 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. If you are having a problem with categorization, use any of the generic headings given above.

fishbone diagram-step-2

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

Brainstorm Possible Causes

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

fishbone diagram-final

You can add these causes horizontally to the fishbone (factors) and label them. You can continue adding sub-branches until you’re satisfied. 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 that you can find the root cause by answering “Why?” five times.

Analyze the Diagram

When your fishbone diagram is complete, 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 have a clear understanding of the problem.
  • Team members should be experienced and involved with the problem.
  • The discussion should be under the project manager.
  • Think of all possible causes for each factor and add them to the fishbone.
  • If any bone is bulky, try to split it into two or three branches.

Benefits of a Fishbone Diagram

  • 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.
  • It involves an in-depth discussion of the problem, which informs the team.
  • It prioritizes further analysis and helps you take corrective action.

Limitations of a Fishbone Diagram

  • A fishbone diagram does not single out the root 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 always effective.
  • If the discussion is not controlled, you can get incorrect results. 

The worthiness of a fishbone diagram depends on the expertise of team members. If they are not experienced, finding the root cause of the problem will be difficult. 

Therefore, be sure to involve experienced experts and ask many “whys.” Up to five “whys” is enough.

Summary

A fishbone diagram is a vital tool in identifying the root cause of a problem. Although 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 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 with us in the comments sections.