The Cause and Effect Diagram

February 10th, 2012

The Cause and Effect Diagram (C&E Diagram), sometimes called the Fishbone or Isjikawa Diagram, is one of the Seven Basic QC Tools. It is a simple but effective way to organize a group or persons knowledge about the potential causes of a problem or issue and display the information graphically. You might want to use this if you want to stimulate the thinking of a group around an issue. Or  so you can see the relationships between different potential cause of an issue or problem.

It was originally created and used by Dr. Kaoru Ishikawa and is sometimes called an Ishikawa Diagram. Also, because of its shape it is called a Fishbone Diagram.

There are several easy steps to constructing a good C&E Diagram, they are as follows:

  1. Develop a team of people that are involved in the process area where this issue or problem occurs. Never try to do this alone because as a team each member brings to the discussion a different perspective of the issue or problem at hand.
  2. Have the team Brainstorm  to find all possible causes of the problem. Remember Brainstorming is a process of collecting ideas. You what as many as you can get even if some seem strange.
  3. Now have the team, using Affinity Diagramming, organize the results into rational categories and sub-categories. Many times getting these categories started or named is difficult so some start with a few basic one at the get go. The four “M’s” are commonly used ( Manpower, Machine, Material, Method) but other are just as good such as environment. As you can see by the diagram above they used Assembly, Process, Fabrication, Design. To them those worked.
  4. Now we start constructing the diagram by Drawing a box on the far right hand side of  a large sheet of paper and draw a horizontal arrow that points to the box.
  5. Inside the box, write the description of the problem or issue you are trying to solve.
  6. Next write the names of the categories above and below the horizontal line. Think of these as branches from the main trunk of a tree.
  7. Then draw arrows from those categories to the trunk ( the horizontal arrow drawn earlier).
  8. After that write in the next level of Sub-Categories and draw in arrow to their main categories. Think of these as limbs and twigs on the branches.
  9. Continue repeating step 8 until all of the sub-categories have been entered.

If you complete this exercise and find a lack of lower level branches and twigs this would suggest the team has a superficial understanding of the problem. In which case you will have to use GIMBA and gather more information.

Once you have this information you need to verify the information you have. Verify by going and collecting data to confirm which of these “potential” causes really do contribute to the issue. Your Diagram may be very large and doing this verification would take to long to do all, so for an alternative the team should prioritize the categories and look at the top few.

Once you have the big hitter then you can start trying to figure out why these occur and a good tool to start with is the 5 Whys.

Well there you have a short article on how to construct and interpret a Cause and Effect Diagrams. Stay in touch as I explain how to construct and interpret Histograms. If, you have questions or comments please feel free to contact me by leaving a comment below, emailing me, calling me, or leaving a comment on my website.

Bersbach Consulting
Peter Bersbach
Six Sigma Master Black Belt
http://sixsigmatrainingconsulting.com
peter@bersbach.com
1.520.829.0090

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