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Quality Glossary Definition: Fishbone diagram

Also called: cause-and-effect diagram, Ishikawa diagram

Variations: cause enumeration diagram, process fishbone, time-delay fishbone, CEDAC (cause-and-effect diagram with the addition of cards), desired-result fishbone, reverse fishbone diagram

This cause analysis tool is considered one of the seven basic quality tools. The fishbone diagram identifies many possible causes for an effect or problem. It can be used to structure a brainstorming session. It immediately sorts ideas into useful categories.

• When to use a fishbone diagram
• Fishbone diagram procedure
• Fishbone diagram example
• Create a fishbone diagram
• Fishbone diagram resources

When to Use a Fishbone Diagram

• When identifying possible causes for a problem
• When a team’s thinking tends to fall into ruts

Fishbone Diagram Procedure

Fishbone Diagram Example

Materials needed: marking pens and flipchart or whiteboard.

1. Agree on a problem statement (effect). Write it at the center right of the flipchart or whiteboard. Draw a box around it and draw a horizontal arrow running to it.
2. Brainstorm the major categories of causes of the problem. If this is difficult use generic headings:
   • Methods
   • Machines (equipment)
   • People (manpower)
   • Materials
   • Measurement
   • Environment
3. Write the categories of causes as branches from the main arrow.
4. Brainstorm all the possible causes of the problem. Ask "Why does this happen?" As each idea is given, the facilitator writes it as a branch from the appropriate category. Causes can be written in several places if they relate to several categories.
5. Again ask "Why does this happen?" about each cause. Write sub-causes branching off the causes. Continue to ask "Why?" and generate deeper levels of causes. Layers of branches indicate causal relationships.
6. When the group runs out of ideas, focus attention to places on the chart where ideas are few.

Fishbone Diagram Example

This fishbone diagram was drawn by a manufacturing team to try to understand the source of periodic iron contamination. The team used the six generic headings to prompt ideas. Layers of branches show thorough thinking about the causes of the problem.

Fishbone Diagram Example

For example, under the heading "Machines," the idea "materials of construction" shows four kinds of equipment and then several specific machine numbers.

Note that some ideas appear in two different places. "Calibration" shows up under "Methods" as a factor in the analytical procedure, and also under "Measurement" as a cause of lab error. "Iron tools" can be considered a "Methods" problem when taking samples or a "Manpower" problem with maintenance personnel. 

Create a Fishbone Diagram

Start using the fishbone diagram template and analyze process dispersion with this simple, visual tool. The resulting diagram illustrates the main causes and subcauses leading to an effect (symptom). 

Fishbone Diagram Resources

You can also search articles, case studies, and publications for fishbone diagram resources.

Books

Business Process Improvement Toolbox, Second Edition

The Quality Toolbox, Second Edition

Articles

Quality Nugget: Creating Ishikawa (Fishbone) Diagrams With R (Software Quality Professional) A fishbone diagram connects causal links in major categories with an outcome, or effect. This article explains how to make one with the Six Sigma package in R.

Fish(bone) Stories (Quality Progress) The method behind the fishbone diagram is older than many of its users. The authors explore how digitizing one of the seven basic quality tools—the fishbone diagram—using mind mapping can significantly improve the tool.

Courses

ASQ Quality Tools - Fishbone Diagram

Continuous Improvement Techniques

Introduction to Lean Principles

Lean Comprehensive

QTools™ Suite

Videos

• Fishbone Diagram
• The Cause and Effect Diagram

Excerpted from The Quality Toolbox, Second Edition, ASQ Quality Press.