A Cause and Effect Diagram is a pictorial diagram showing possible causes (process inputs) for a given effect (process outputs) It is also referred to as the “Ishikawa diagram” or “fishbone diagram.
Created by Kaoru Ishikawa (1968) that show the causes of a specific event. Common uses of the Ishikawa diagram are product design and quality defect prevention, to identify potential factors causing an overall effect.
Each cause or reason for imperfection is a source of variation. Causes are usually grouped into major categories to identify these sources of variation. The categories typically include: (Also see the 5Ms and 1P)
- People: Anyone involved with the process
- Methods: How the process is performed and the specific requirements for doing it, such as policies, procedures, rules, regulations and laws
- Machines: Any equipment, computers, tools, etc. required to accomplish the job
- Materials: Raw materials, parts, pens, paper, etc. used to produce the final product
- Measurements: Data generated from the process that are used to evaluate its quality
- Environment: The conditions, such as location, time, temperature, and culture in which the process operates
Fishbone Best Practices
- Focus on cause, not solutions.
- Go beyond the superficial levels to find root causes. Don’t merely outline options.
- Ask “why” until it is absurd to continue.
Fishbone Diagram videos
Minitab put out a good video on how to use their software to brainstorm and create a fishbone diagram. If you’ve never done this before, this is a great reference.
ASQ Six Sigma Black Belt Exam Fishbone Diagram Questions
(Taken from ASQ sample Black Belt exam.)
Question: A company’s accounts payable department is trying to reduce the time between receipt and payment of invoices. If the team has just completed a flow chart of the process and identified the critical steps, which of he following tools should be used next?
A) Fishbone diagram
B) Scatter diagram
C) Box and whisker plot