What is Root Cause Analysis

The process of finding out the fundamental flaw or "root cause" as to why a problem or defect has occurred is called Root Cause Analysis. Once such an event is pinned down, it can be planned for probabilistically in the future, and hopefully prevented from reoccurring, or at least have its effects minimized. This is an important component of Design Theory.

All sorts of root cause analysis software and tools have been created in order to perform root cause analysis.  Some of these tools are the Pareto chart, failure mode and effects analysis (FMEA), and the fishbone diagram.  While all of of these tools are useful, in this article, the fishbone diagram will be looked at more closely.

Root Cause and Effect

The fishbone diagram has few other names such as the cause and effect diagram, 5-Whys chart, and the why-why diagram.  These names are appropriate because this tool seeks to find the reasons why a particular event (the effect) was caused.

The general process for completing the analysis is to begin by identifying the end effect and working backward, toward the ultimate, or “root” cause.  Typically this is the event or defect for which one is trying to determine the cause.  The next step in the process is to identify the cause of that effect.  This is often accomplished by asking the question, "Why did this effect happen?"  Several different answers may be generated and such a list should be anticipated.  Once these answers are discovered, you ask the question, "Why did this cause happen?" for each of the causes generated in the previous step.

5 Why’s Technique

Using the "5 Whys" technique will lead to the root cause of a condition. To document what this technique looks like, the condition being investigated is listed on the right side of a piece of paper or on a display. Draw a horizontal line to the left. Ask "why" the condition occurred and note on a line coming off the horizontal line at a tangent the answer to "why". Continue doing this until 5 Whys are asked. The tangent lines will resemble a fishbone which is what this process is frequently called.

An example of the 5-why chain for a company which has just lost a customer follows.  The company lost its customer because the price was too high.  The price was too high because the assembly process took longer than it should have.  The assembly took too long because the workers didn’t have the correct tools.  They didn’t have the correct tools because the tools weren’t ordered.  The tools weren’t ordered because upper management was hoping to cut costs for the quarter.

After the root cause is uncovered, measures may be taken either to either guarantee that the root cause can be prevented in the future if the end result was a negative one, or else that it occurs again if there was a positive result. Only the symptoms of the problem get treated, as opposed to the cause, if the core of the problem is not correctly identified. Practices such as these could bring on extra costs, slower delivery, lesser quality, or all three.

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