Named after Kaoru Ishikawa, and also called the Cause-and-Effect diagram, the Ishikawa diagram is a brainstorming tool that engages in identifying causes for a particular problem. As the name suggests, it is a diagrammatic tool, where the process of braingstorming and thinking results in a diagram representation of the causes of a known effect.
There are two sections of the diagram; the right side has a box specifying the problem under analysis. A line is then drawn from the box extending towards the left. All possible causes suggested in the course of the brainstorming are then drawn as arms extending out from this main line. Causes can also be differentiated under different categories, with each category having it's own sub-branches. This gives the diagram a fishbone appearance, hence the diagram is also called a Fish-Bone diagram.
As a guideline, the ASQ recommends using the 6 Ms, Machine, Method, Materials, Maintenance, Man, Mother Nature (Environment), as basic categories for brainstorming. This of course does not prevent from identifying further categories.
Another technique to trigger brainstorming is "5 Whys" which involves repeatedly asking the question "Why?!" until the result is drilled down to specific, measurable, controlable causes.
The Fishbone diagram can be used when possible causes of a problem need to be identified, using peoples' thinking. Advantages of using Fishbone diagram are that the problem is clearly identified, multiple causes are identified and inherently classified, people are invovled in the generation of ideas and the output is a visual representation of the ideas.
The best situations to use the Ishikawa diagram are when root causes to known problem need to be identified by stimulating thinking and brainsotrming among a group of participants.
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