Cause and Effect Diagram | Fishbone Diagram | Case Study

What is a Cause and Effect Diagram?

→ Cause and effect diagram represents the meaningful relationship between an effect and its causes.

→ It is an excellent tool for root cause analysis.

→ This tool is one of the most important of the 7 Quality Control Tools.

→ Dr. Kaoru Ishikawa developed this diagram in 1943 during consulting for Kawasaki Steelworks in Kawasaki Shipyards so Dr. Joseph M. Juran named it "Ishikawa".

→ This diagram is also known as a "Fishbone Diagram" because it looks like the bone of a fish.

Table of Contents:

• What is a Cause and Effect Diagram?
• History
• Different Names of Cause and Effect Diagram:
• When to use a Cause and Effect Diagram?
• Why to Use the Fishbone Diagram?
• Elements of Fishbone Diagram:
• How to Conduct Fishbone Analysis?
• How to Make a Cause and Effect Diagram? 
• Benefits
• Conclusion

History:

→ Refer to the below-mentioned key milestones of the cause and effect diagram.

→ In the year 1920s: During this time the basic concept of cause and effect diagrams emerged.

→ In the year 1960s: Kaoru Ishikawa, a Japanese management consultant used these diagrams extensively during his tenure with Kawasaki Heavy Industries. Due to his contributions, the cause-and-effect diagram is known as the Ishikawa diagram.

→ In the year 1968: In this year Ishikawa formally introduced the cause and effect diagram.

→ In the year1980s: The concept gained further recognition as part of the 7 QC Tools.

Different Names of Cause and Effect Diagram:

→ Refer to the below-mentioned different names of the Cause and Effect Diagram:

• Ishikawa diagram
• Fishbone Diagram
• Herringbone diagram
• Ishikawa-Fishbone diagram
• Herringbone
• Fishikawa
• 8P Fishbone
• 6M Fishbone

When to use a Cause and Effect Diagram?

• For identifying possible causes of an issue.
• It is used for root cause analysis.
• This tool is very helpful during a Lean Six Sigma Project.
• It is used for problem identification and analysis.
• To check the relation between cause and it's effect
• Improve output quality and efficiency
• Brainstorming during problem-solving
• To improve the quality of a product

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Why to Use the Fishbone Diagram?

• We can use the fishbone diagram for the following things:
• Helps to determine the root cause of a problem.
• Group participation & knowledge sharing. 
• Indicates possible cause for variation in a process. 
• Increases knowledge of a process, its factors, etc. 
• Identifies areas of further data collection

Elements of Fishbone Diagram:

→ The fishbone diagram has three main parts that are explained below.

⏩ The three elements of the fishbone diagram are:

1. Head
2. Backbone
3. Bones

→ Now we will learn one by one in detail.

(1) Head:

→ The head of the fish is where we mention the problem or outcome during analysis.

→ It is the right side part of the diagram.

(2) Backbone:

→ Backbone is the middle part showing as a straight line and it looks like a bone of fish.

→ The backbone simply provides a way to connect all the other bones to the head or main problem.

(3) Bones:

→ The bones represent all the different causes or sub-causes.

→ The bones could be leading to the main problem.

→ In this diagram, we need to identify some main categories of causes(s).

→ So we need to arrange all causes as per the categories.

How to Conduct Fishbone Analysis?

→ First of all we need to prepare one cross-functional team.

→ Then we need to identify and define the problem on which we need to work.

→ Write the problem or effect statement in a box at the center-right on paper or board.

→ Draw a long horizontal line pointing to the box.

→ Identify the cause categories using the 6 Ms, 8Ps, or 4Ss approach.

→ Notedown into the boxes that are parallel up and down to the center line.

→ Now we will brainstorm to identify all the possible causes as per categories.

→ We will start with the main causes and then the secondary causes and so on Use 5 whys to get to the root causes.

→ Now we need to assign numbers to the key causes to show their relative importance.

→ Draw links between causes that are related.

→ Now we need to validate the cause based on data.

→ After validation, we need to prepare an action plan and implement actions to eliminate causes and problems.

How to Make a Cause and Effect Diagram? 

→ Four Steps to construct a cause and effect diagram are:

1. Define the undesirable effect or problem
2. Identify the main cause groups
3. Arrange causes and sub-causes
4. Identify potential root cause(s)

Step 1. Define the undesirable effect or problem:

→ First of all, we will mention the undesirable effect or problem and draw the backbone and a line.

→ Then define a problem statement (effect).

→ Write it at the center-right of the chart or whiteboard.

→ Draw a box around it and draw a horizontal arrow running to it.

→ For better understanding, we are taking one example for root cause analysis for this we will prepare the backbone and line as mentioned in the below picture.

Step 2. Identify the main cause groups

→ In the second step, we brainstorm the major categories of causes that are related to the problem.

→ For the manufacturing industry, it is "6M".

⏩ 6M's of Fishbone Diagram are:

1. Man/People
2. Machine
3. Material
4. Method
5. Measurement
6. Mother Nature / Environment

➨ For the marketing Industry "6M" is replaced by "8P".

⏩ 8P's of Fishbone Diagram are:

1. Product (or service)
2. Price
3. Promotion
4. Place
5. Process
6. People (personnel)
7. Physical evidence
8. Performance

➨ For the Service Industry "6M"  is replaced by "4S".

⏩ 4S's of Fishbone Diagram are:

1. Surroundings
2. Suppliers
3. System
4. Skill

→ Now we are taking an example of the poor mileage of cars to understand the concept of root cause analysis for this we are taking 6M then we will remove the irrelevant "M" from "6M".

Step 3. Arrange causes and sub-causes:

→ Now we are moving forward by taking the problem of poor mileage in the car.

→ Write the categories of causes as branches from the main arrow

→ Brainstorm all the possible origins of the problem.

→ Ask: “Why does this happen?” As each idea is given, the facilitator writes it as a branch from the appropriate category.

→ Study all probable causes that are related to poor mileage of the car.

⏩ Probable causes of poor mileage are:

• Carburetor adjustment
• Underinflated tire
• Poor maintenance
• Poor driving habit
• No awareness
• Improper lubrication
• Wrong fuel mixture
• Engine oil grade is not proper
• Gear shifting is not in sequence
• Wrong gear shifting
• Drive too fast

Step 4. Identify potential root_cause(s):

→ Again ask “Why does this happen?” about each cause.

→ Write all the things with the main branch and sub-branch.

→ Continue to ask “Why?” and generate deeper levels of problem origin.

→ After validation of all probability, we will get the reason for poor gas mileage in the car is poor maintenance of the car which you can easily understand from the below example.

Benefits

• Helps to determine the root cause(s)
• Increase Process Knowledge
• Encourage group participation
• A good tool for brainstorming
• Identifies areas for collecting data
• It is a structured tool for problem-solving
• Improve Team Collaboration
• Enhance Problem-Solving Efficiency

Conclusion:

→ The fishbone diagram is very easy to use and a very well-structured diagram.

→ We can easily identify any underlying issues and prepare appropriate action to overcome those issues.

→ This tool provides a clear path for any problem within or outside the organization that has a business impact.

→ In easy language, we can understand this tool in very simple steps such as Define the Problem, Identify Major Categories of Causes, Brainstorm Possible Causes, and Analyze the Diagram.