ASQ — Seven Basic Quality Tools: The Fish Bone Diagram (4)

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This fourth article introduces the fishbone diagram, also known as the Ishikawa or cause-and-effect diagram, which is tool that identifies many possible causes for an effect or problem. It can be used to structure a brainstorming session so as to immediately sort ideas into useful categories for further examination. And yes, it looks like the skeleton of a fish.

This series of articles presents the 7 Basic Quality Tools for Process Improvement used in the field. These are defined as instruments or techniques to support and improve the activities of quality management and improvement. ASQ has made available to the members and the public a huge amount of information on the "quality" body of knowledge (BOK). It is only meant to be a starting point, but oh so useful.

When to Use a fishbone diagram:

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

Create a fishbone diagram:
Read the full article on preparing a fishbone diagram then, pull-out a flip chart or whiteboard and markers. You can also use the following fishbone diagram template. This simple visual tool also allows you to analyze process dispersion. The resulting diagram illustrates the main causes and subcauses leading to an effect (symptom).

Basically, your team must first agree on a problem statement (effect). Write it at the centre right of the flip chart or whiteboard, draw a box around it and then draw a horizontal arrow running to it (fishbone, see the example). The team then brainstorms the major categories of potential causes of the problem. They will typically fall into the following generic headings: Methods; Machines (equipment); People (manpower); Materials; Measurement and Environment. These serve as branches from the main bone. The team brainstorms all the possible causes of the problem (ex. "Why does this happen?") and the facilitator writes it as a branch from that appropriate category. Note that causes can be written in several places if they relate to several categories. Sub-causes branching off the 'main' cause could also be identified, generating deeper levels of causes. Layers of branches indicate causal relationships. As the group runs out of ideas, focus attention to places on the chart where ideas are few.

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In the example above, 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.

§ This News post was adapted by J.P. Amiel, ASQ Senior, CQA ret., Web committee Chair, from content at ASQ's Quality Resources pages, which are excerpted and adapted from The Quality Toolbox, Second Edition, ASQ Quality Press.

History: Kaoru Ishikawa is considered a key figure in the development of quality initiatives in Japan, particularly the quality circle (a team problem solving approach). He is best known outside Japan for the Ishikawa, fishbone or cause and effect diagram, often used in the analysis of industrial processes. (Wikipedia)


ASQ References:

Quality tools  ► Quality tools A to Z  ► Download quality templates and Excel tools  ► Quality tools resources  ► Quality glossary

Kaoru Ishikawa – Born : 13 July 1915 in Tokyo, Japan; Died : April 16, 1989 (at 73) :  • American Society for Quality Biography  • Description Wikipedia


Here is a list of the articles in this series:

Article Title
ASQ — Seven Basic Quality Tools: The Series
ASQ — Basic (And Not So Basic) Quality Tools Resources
ASQ — Seven Basic Quality Tools: The Check Sheet And The Histogram (1)
ASQ — Seven Basic Quality Tools: The Pareto Chart (2)
ASQ — Seven Basic Quality Tools: The Control Chart (3)
ASQ — Seven Basic Quality Tools: The Fish Bone Diagram (4)
ASQ — Seven Basic Quality Tools: The Scatter Diagram (5)
ASQ — Seven Basic Quality Tools: Stratification (6)
News Montreal Section 10/03/2022 10:01am CDT

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