Cause and Effect Diagrams

 

Fishbone Diagram

Introduction

Ishikawa diagrams (also called fishbone or cause and effect diagrams) were developed by Kaoru Ishikawa in the 1960s. He developed the diagram as a quality management tool to illustrate the relationship between an outcome and its proposed causes. The diagram assists:

• determine the root cause
• encourage group discussion
• sharing ideas of possible causes in an easy to read format
• identifying relationships between possible causes and / or causal sequences
• identifying areas where information and knowledge is poor

 

How to create a fishbone diagram

Step 1. Clearly define the effect to be analyzed. The effect can be stated an problem to be solved or an objective to be achieved.

 

Step 2. Draw an arrow pointing to the effect.

 

Step 3. Think of some of the main categories of causes. The following are examples of possible categories: 

 

The original 4 M's

• Machine (Equipment)
• Method (Process/Inspection)
• Material (Raw,Consumables etc.)
• Man power

The 8 P's (Used In Service Industry)

• People
• Process
• Policies
• Procedures
• Price
• Promotion
• Place/Plant
• Product

The 4 S's (Used In Service Industry)

• Surroundings
• Suppliers
• Systems
• Skills

Write the main categories to the left of the effect and well above and below the main arrow. 

 

Step 4. For each of the main categories identify causes relating to the category.

 

Step 5. Explore each of the possible causes and look for what might cause them in their turn.

 

Step 6. Analyse the diagram:

• Which categories are showing many possible causes?
• Area there categories that need further investigation?
• Can some of the possible causes be tested?