CI Tools

What is 5 Why analysis? How to use 5 Why and Fishbone diagram for root cause analysis.

One of my favorite tools for root cause analysis is 5 Why.  I like it because it is simple, and you can use it anywhere, and for any situation.  You don’t need to do complicated analysis, take notes or draw anything, you only need to keep your brain asking why until you find the root cause for the problem.  It is also very helpful to see the relationship between different causes. 

This tool is simple but requires practice.  The number of times you ask why depends on each particular situation; five it is not a number written on stone.  If you stop asking why too soon, you will end up far away from the real root cause and asking too many times result in complaints or non-sense answers.

Most of the time the root cause of a problem falls into one of these categories

  1. No standard or inadequate standard
  2. Not following the standard
  3. Inadequate system or equipment

These are the steps to do a Five Why analysis.

  1. Define the problem.
  2. Start describing the problem using all details from the problem definition.
  3. Ask why the problem happens, this is the answer to your first why.
  4. If the answer does not identify the root cause, ask why again.  This is the answer to this why.
  5. Keep repeating the fourth step until you identify the root cause.

My last post was about fishbone, another tool that I used very often.  I like to use it to explore all possible causes because it helps to force people to think beyond the obvious reasons.  Once you complete the cause and effect diagram, you should end up with one or two causes.  At this point, you can use the 5 Whys to drill down the root causes.  

The fishbone I used is from an analysis completed in a food manufacturing plant.  We were looking for the cause of getting excess oil in the body of cans containing oil products.  The fishbone analysis results in two possible causes, both of them related to the equipment used to wash the cans.  The causes were the alignment of the detergent nozzles and the quantity of soap dispensed.  We used the 5 Whys to determine the root cause of each, and we find that the reason was that there was no standard for the setting of the equipment.

Most of the time, when a problem happens, the first thing you see is a symptom.  In this example, the symptom was oily cans.  Without root cause analysis, most probably we would stop at insufficient training, but with fishbone and 5 Why we were able to drill down to the ugly truth, a standard was never established.

Now you have two simple and effective tools to use to find the root cause of a problem.  Practice PDCA and use these tools for RCA, you will see the difference between traditional and lean problem-solving.