The Ishikawa diagram is a graphical method for finding the most likely causes for an undesired effect. The method was first used by Kaoru Ishikawa in the 1960s.

Because of its shape, it is also known as the fishbone diagram. Another name for this technique is: the cause-and-effect diagram. The fishbone diagram is a method/tool used in a root cause analysis.

The Ishikawa diagram is one of the seven basic tools of quality control, which include the histogram, Pareto chart, check sheet, control chart, cause-and-effect diagram, flowchart, and scatter diagram. See Quality Management Glossary.

An alternative use of the fishbone diagram is in product design, to identify desirable factors leading to an overall effect. Mazda Motors famously used a fishbone diagram in the development of the Miata car, where the required result was "Jinba Ittai" or "Horse And Rider As One". The "main bones" included such aspects as "touch" and "braking" with the smaller bones including highly granular factors such as "50/50 weight distribution" and "able to rest elbow on top of driver's door". Every factor identified in the diagram was included in the final vehicle.

How to make the diagram

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Take a sheet of paper and draw a box half way down the sheet on the right. Draw a horizontal line from the left side of the box to the left side of the sheet. Write in the box the effect for which you want to find the causes. Starting from the horizontal line, draw four to six short diagonal lines in the direction of the top left corner and bottom left corner of the paper. These are the main bones of the diagram. Label them with categories you know will span the whole problem space. For example, a business may use: management, manpower, machines and materials (the 4 M's).

Next, start filling the diagram with causes. Put them as arrows pointing to any of the main bones of the diagram. After you feel you have named most causes, identify the most likely causes for the effect in the box on the right side.

External links

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• http://mot.vuse.vanderbilt.edu/mt322/Ishikawa.htm
• http://c2.com/cgi/wiki?FishboneDiagram
• http://www.skymark.com/resources/tools/cause.asp

Knowledge representation | Diagrams | Quality control tools

Ursache-Wirkungs-Diagramm | Diagrama de Ishikawa | Diagramme de causes et effets