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What is the fishbone diagram? Problem-solving using the cause and effect analysis to find the root cause.

Problem-solving is the process of finding a solution to a problem.  ASQ defines problem-solving as the act of defining a problem; determining the cause of the problem; identifying, prioritizing, and selecting alternatives for a solution; and implementing a solution.  It sounds complicated, and it is complicated.  After all, we are looking for an often-elusive solution for complicated and recurrent problems.

There are various problem-solving methodologies, PDCA, DMAIC, 8D, and others.  The effectiveness of all of them depends on the definition of the problem and finding its root cause.  Tools like fishbone analysis, or the 5 Why facilitates the process to find the root cause.

Today, I will focus on the tool commonly known as the fishbone diagram, but it is also known as Ishikawa Analysis or Cause & Effect diagram.  The diagram looks like a fishbone, with the problem description at the head and five categories as bones attached to the fish backbone.  The categories are the five M’s; material, manning or personnel, method or process, measurements, machine, or equipment.  Some people add a sixth category, environment, or mother nature.

The steps to complete the Ishikawa analysis are the following.

  1. Define the problem.
  2. Identify the major factors or categories, you can use your categories, or some of the general categories indicated above.
  3. Brainstorm possible causes with the team
  4. For each cause identified, continue to ask “why” that happens and attach that information as another bone of the category branch. You can see an example in the fishbone above, in the category machine.
  5. Construct the actual diagram
  6. Analyze to find the most basic causes of the problem, look for causes that appear repeatedly.
  7. Reach team consensus

The goal of RCA is to identify one or two reasons, that, if corrected will reduce recurrence.  The rule of thumb is that if there are three or more root causes, you can assume the root cause has not yet been found, and you need additional investigation.  In summary, keep digging!

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