Kaoru Ishikawa created the Cause and Effect Diagram in 1943 to do just this in order for Kawasaki Steel Works engineers to understand how factors related to their work might be sorted and associated. Because of his involvement in the creation of the cause and effect diagram, these charts conveying all-too-important relationships  between seemingly disconnected elements in a system are frequently referred to as Ishikawa diagrams. In some circles, they are also referred to as fishbone diagrams, since at certain stages of their drawing, they look a bit like, well, fish bones.

How to Use Cause and Effect Diagrams

Few quality-related problems are easily resolved. More frequently, various causes intermix in unique and complicated ways to produce the final negative impact upon quality one wishes to improve. The use of a cause-and-effect diagram allows you to:

• Define and display the fundamental causes, related causes and root causes that impact a system, process or outcome this process is frequently referred to as fishbone analysis,
• Provide the focal point to discuss alternatives and come to a joint conclusion on appropriate remediation,
• Understand  the potential interrelationships of various causes which ultimately lead to the symptomatic defects or noted issues,
• Measure and Improve process flows and during in the Lean Six Sigma methodology,
• Provide a focus for Kaizen Blitzes in order to focus on the highest value efforts.

Cause and Effect Diagram - How To

	Determine which undesirable outcome, negative effect, or quality characteristic  you intend to investigate. In many cases, a Pareto Analysis will make sure your efforts are focused on the highest Return on Investment (ROI) for your efforts.
	Write out your selected final effect or root cause analysis subject on the right hand side of your writing surface.  In a meeting or such, this would be a whiteboard or stick pad.  You might decide to do this in Visio, Word, PowerPoint, or with special charting software, if you so choose.  In a fishbone diagram, this is the head of the fish.
	From the center of the effect, draw a line straight off to the left, creating the backbone of the fish.
	Draw a line slanting diagonally outward from the spine of the cause and effect diagram away from the head of the diagram. Each of these lines represents a major cause factor or cause, in itself, lending toward the final effect.
	For each secondary cause or attribute of a cause, draw a line horizontally, intersecting with the related diagonal line.  Alternate these on either side of the cause line.
	Similarly, further attribution of cause can be done with smaller and smaller lines stemming from lines of greater significance.  If you find that parts of the diagram have, through the brainstorming process, a better placement in another part of the cause and effect diagram, move them where appropriate so that the end effect of “seeing the whole picture” is maintained.
	Examine your cause and effect diagram for causes of significance, correlation, greater occurrence, greater impact, and sadly, in some situations, greater political value. Identify those causes which are more important as such.

Tips to Make Your Fishbone Diagrams Sparkle

• Involve as many people as possible in the process of brainstorming. Not only will your diagram end up being far more complete, but the value of the knowledge your team gains  will be quite invaluable.  Further, the participants will have a feeling of ownership in the root cause analysis process, and feel far more willing to pursue whatever remediation is concluded as a result of the experience.
• For each of your Critical-To-Quality (CTQ) characteristics you’re working through, create a unique cause-and-effect diagram.  Putting too many problems into one cause and effect diagram will create far too unwieldy a product to actually be of value.
• Express each of the identified causes as specifically and accurately  as possible. In order to leverage the cause and effect diagram as a diagnostic tool for isolating causes and through cause-and-effect relationships, every factor, cause, and sub-cause should be as measureable as possible.  When a more measurable substitute can be used, do so.
• The goals of your creating this cause-and-effect diagram is to take action toward resolution. Be absolutely certain that your identified causes are decomposed to a level that they can be actively resolved.

Now what?

Now that you’ve created your Cause and Effect Diagram, what do you do with it?

• Use your cause and effect diagram to develop a common understanding across the organization of the various contributing factors which impact the given quality problem  or characteristic.
• Use the finished diagram to chart a course for future efforts, improving your data collection efforts around any of the softer factors identified in the brainstorming process.
• Maintain the diagram as a living document, updating it as remediation planning begins and as solutions to problems uncover more details than were available at the initial whiteboarding sessions.
• Continually examine high impact causes and sub-causes for possible optimization, looking for opportunities to modify or eliminate errant processes.

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