Manufacturing Breakthrough Blog

Six Sigma and the Causal Chain

Tuesday March 10, 2015

Problem Solving

Over the course of time, every organization has experienced problems.  Sometimes the problems are solved with simple solutions, while other times the problem requires an in-depth analysis before it can be solved.  One thing is for certain, in order to solve any problem, simple or complex, we must know the root cause of the problem.  Unfortunately many organizations and people tend to treat the symptoms of problems rather than the true root cause.  And when this happens, the problem never really goes away.

A Causal Chain Example

While Six Sigma offers a variety of tools, one of my favorites is called the Causal Chain.  I like this tool because, as you will see below, on a single sheet of paper, we are able to see the cause and effect links of the various symptoms leading to the ultimate root cause.  A causal chain is the path of influence running directly from the apparent problem to the ultimate root cause and the symptoms we see in between the two.  In other words, a causal chain is an ordered sequence of events that link the causes of a problem with the effects of the problem.  Each new link in the causal chain is created by repeatedly answering the question “Why?” At the end of the connected links lies the root cause of the problem.

The causal chain begins with the identification of the problem.  The chain is constructed by placing the object/entity with the problem above the line with the state that it’s in being place directly beneath the object/entity.  For example, if you were to find that an extruded product is too wide, you would write it as “extruded product” on top and directly beneath it you would write “too wide.”  You would then ask the question "why?" and record the response accordingly.  If there are multiple potential answers to the question, then record all of them in a structured way as follows:

In this example, we are looking at an extruder that is extruding a product to a specific width.  As you can see, the identified problem is that the product width is too wide.  You ask the question, why is the product width too wide?  In this causal chain I have listed three answers to this question:

  1. Product cutting guide is loose
  2. The guide width is set too wide
  3. The product expansion is greater than it should be

There may be more potential causes, but for demonstration purposes I have only listed these three.  For each new answer to the “why” question, you can look at that part of the chain and see if the predicted effect exists in your reality.  If it does, you can correct it and move on to the next effect.  If the effect no longer exists after you have corrected it, then you have solved the problem.

You can also have more than one effect in your causal chain as demonstrated in the figure above.  If you have thought through the entire potential cause and effect relationship, then at the end of the chain lies the true root cause or causes.

A Question to Ponder

Next Time

In my next posting we will discuss another very useful tool in the Six Sigma tool kit, the Cause & Effect Diagram.  Like the causal chain, the C & E diagram is a very useful tool for identifying potential root causes.  As always, if you have any questions or comments about any of my postings, just leave me a message in the box below and I will respond. 

Thanks for reading. Until next time.

Bob Sproull


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