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RCA and Ishikawa Diagrams

Posted by admin on March 3, 2014

We are often asked about various problem-solving techniques and how they compare to the root cause analysis (RCA) process we help our manufacturing clients integrate into their operations.  In many cases, our client or prospect has tried these popular techniques and found they come up short in helping the company in resolving problems effectively and efficiently.  One of the techniques we are asked about often is Ishikawa diagrams. 

First off, we think any problem solving approach is better than the pure trial-and-error approach to problem solving that can cost a manufacturer valuable resources and customer relationships.  Using a common approach aids in communications and providing information that can eventually be used to identify the true cause and the best fix for the problem.  Without this, companies go through guesswork or apply band aids to keep production going, not knowing what new problems these temporary maneuvers may cause.

Ishikawa diagrams (also called fishbone diagrams or cause-and-effect diagrams) show the possible causes of a certain event.  Common uses of the Ishikawa diagram are productdesign and quality defect prevention, to identify potential factors causing an overall negative effect.  Each cause or reason for imperfection is a source of variation.  Causes are usually grouped into major categories to identify these sources of variation. The categories typically include:

  • People - anyone involved with the process
  • Methods - how the process is performed and the specific requirements for doing it, such as policies, procedures, rules, regulations and laws
  • Machines - any equipment, computers, tools etc. required to accomplish the job
  • Materials - raw materials, parts, etc. used to produce the final product
  • Measurements - data generated from the process that are used to evaluate its quality
  • Environment - the conditions, such as location, time, temperature, and culture in which the process operates

Some of our clients who have used Ishikawa diagrams have voiced concerns that this technique provides too broad a list of possible causes to be investigated.  Each of these possible causes requires considerable testing to home in on the most likely cause.  They prefer the ASG RCA process because it uses effective questioning to help the problem solver, or team, more quickly eliminate unlikely causes so they can focus on a shorter list of possible causes.

Clients’ other frustration with Ishikawa is that even when they get to the true cause, Ishikawa may not help them implement the fix to that cause or think about what could go wrong with the fix that may cause other problems.  Our RCA approach takes the problem right through to resolution in developing the corrective action, considering what could go wrong with that action, ways to prevent that from happening and how to mitigate any negative impacts.  

The best approach may be to not consider any one problem solving approach as the best for every situation.   For example, the Ishikawa method can be helpful when there is absolutely no clue to the cause of the problem and the team is trying to generate a full list of possible causes to be considered.   Once the Ishikawa list is developed, the RCA process can be used to test the causes, identify the true cause and corrective action, and implement the fix.   This approach can use a strength of the Ishikawa method and the comprehensiveness of the RCA process to get to problem resolution. 

In the coming months we will look at other popular problem-solving techniques and the benefits and drawbacks of each.  The focus is on how these techniques can be used most effectively to generate true results.