Fishbone Diagram (Cause and Effect Diagram)

Fishbone Diagram

Fishbone Diagram-Brainstorming
Fishbone Diagram-Brainstorming

Fishbone Diagram (Cause and Effect Diagram)

Fishbone diagram (cause and effect diagram or Ishikawa diagram ) is a quality management tool that is used to identify the root cause of a problem. It analyzes various possible causes of a problem by the help of brainstorming sessions. This article reviews the Fishbone diagram (cause and effect diagram or Ishikawa diagram ) as a problem solving tool and discusses the advantages and limitations of it.

Concept of the Fishbone Diagram (Cause and Effect Diagram or Ishikawa Diagram)

The concept of the Fishbone Diagram was developed by a Japanese Professor, Dr. Kaoru Ishikawa in the 1960’s. The Fishbone diagram looks like a fish skeleton so that it took it’s name from it’s appearance. It is also named as “Ishikawa Diagram”.

It is a visual quality management tool that provides an overall list of possible causes to determine the root cause of a specific event. Each defect or cause is a source of variation. It helps to understand what causes a problem and what are the possible ways to solve it.

The Fishbone Diagram (Cause and Effect Diagram or Ishikawa Diagram) is one of the seven basic tools of quality.



What are the Seven Basic Quality Tools ?

The seven basic quality tools are graphing techniques that people commonly use for quality control management purposes. They are easy to use and implement.

  1. Fishbone Diagram (Cause and Effect Diagram or Ishikawa Diagram)
  2. Check sheet
  3. Control charts
  4. Histogram
  5. Pareto chart
  6. Scatter diagram
  7. Stratification

Categorization of Causes in a Fishbone Diagram

Fishbone (cause and effect diagram or Ishikawa diagram ) are used in may industries such as service, manufacturing, marketing and construction. Causes of problems may arise from typical categories based on the industry. Below are a few suggested categories for some industries. They may be helpful to create the framework.

Service Industries



In the service industry, you can categorize the factors (causes) by 4Ps:
• Policies
• Plant/Technology
• Procedures
• People

Manufacturing Industries

In the Manufacturing industry, you can categorize the factors (causes) by 6Ms:
• Material
• Manpower
• Measurement
• Mother Nature (Environment)
• Management
• Machine

Marketing Industries



In the Marketing industry, you can categorize the factors (causes) by 7Ps:
• Place
• Promotion
• People
• Packaging
• Product
• Price
• Positioning

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)

Once all the project team agreed on the problem, the problem expression can be written in a box at the mouth of the fish.

Fishbone Diagram-Identify the Problem (Effect)
Fishbone Diagram – Identify the Problem (Effect)

2. Define the major categories of causes for the Problem

Major categories can be defined by the help of brainstorming sessions. Then, the major categories can be written as branches from the main arrow. Major categories often include: Material, Manpower, People etc.

Fishbone Diagram-Major categories
Fishbone Diagram – Major categories

3. Brainstorm all the possible causes



In this step brainstorming can be made by group/team members based on their prior experiences. During brainstorming, ask “Why does this happen?” Then note the answer.

Write the causes horizontally to the fishbone where they belong. If the causes are related with various categories, you can write them in several places.

Then, ask again “Why does this happen?” for each cause. Write sub-causes branching off the cause branches.

Fishbone Diagram-Brainstorming
Fishbone Diagram -Brainstorming

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

Below are a few benefits of the Fishbone Diagram (Cause and Effect Diagram or Ishikawa Diagram).

The Fishbone Diagram;

  • Is a visual tool which displays the links and relationships among the potential causes and results displayed in the diagram.
  • Demonstrates all causes simultaneously.
  • Encourages brainstorming about the reasons for a certain result because it captures all the causes.
  • Stimulates your team to explore the root cause of a problem.
  • Improves decision making within the project team.
  • Helps to determine the methods to improve the process and take corrective actions.

Limitations/Drawbacks of a Fishbone Diagram

Below are some of the limitations of the Fishbone (Cause and Effect Diagram or Ishikawa Diagram).



  • For a realistic result, a skilled team is required 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 the team members bias.

Summary



The fishbone diagram is a powerful process improvement technique which greatly helps to determine the important factors involved in a process. It is one of the seven basic tools of quality widely used for problem solving. In order to use this technique, create a team and agree on the problem. Then, define the categories of causes related with te problem and start brainstorming sessions. Brainstorming provides different point o views that you can take advantage of team members experiences. Five whys technique can be used during brainstorming sessions. Creating this diagram encourages teamwork and builds trust between departments. It is widely used in all industries as a problem solving tool.

External References

[1] American Society for Quality

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