5 Whys and Root Cause Analysis
From Toyota Motor Corporation
“Underneath the “cause” of a problem, the real cause is hidden. In every case, we must dig up the real cause by asking why, why, why, why, why. Otherwise, countermeasures cannot be taken and problems will not be truly solved.”
As the great Sensei Taiichi Ohno teaches us, the “5 Whys” are there to help us look underneath the cause of a problem to find the “real cause” so that we can find solutions that will prevent the problem from happening again.
And, although the five whys technique can work for both Operations-related problems and Service-related problems it is important to understand the strengths and limitations of this approach as well. Think of it as a very important tool in your Lean Toolbox, but you’ve also got to remember to use the “right tool for the right job.”
Here are 3 things that can help you improve your 5 Whys:
1. Consider where the problem is happening and investigate possible factors that lead to the problem using a Fishbone Diagram. A Fishbone diagram is a great tool to help you look at potential areas – by helping you to categorize and organize these factors in a way that will allow you to cover a lot of areas while avoiding repetition. There are a number of configurations that will allow you to divide up specific “cause categories” – here are 2 that are quite popular:
4M: Man, Machines, Materials, Methods6P: People, Processes, Priorities, Programs, Products
2. Gather facts and confirm them through Genchi Genbutsu. For your root cause analysis to be robust, it is always important to verify your facts by going to the Gemba. Observe the actual situation in the actual place that it occurs (by far the best way) and if you speak with people, use active listening to do your best to understand the content and to clarify whether you are hearing opinion or fact. This is a good time to remember that it is always important to avoid the “5 Whos” – in other words, rather than blaming people, focus on the “Whys”. Don’t forget that more often than not a certain behavior that is out of standard may be due to reasons beyond what meets immediately meets the eye.
3. Make sure you’ve found the root cause. Often the question is “when will I know I have found the root cause? – is it automatically at the fifth “Why”? First of all, the number 5 is a rule of thumb – sometimes it may take less “whys”, maybe it will require more. The most important thing is to keep digging deeper, beyond the source of the problem. One way to test whether you have found the root cause is to ask yourself, if I eliminate this, will it solve the original problem?
Hint: We often utilize an image of a funnel – where each new “Why” question gets us closer to the end of the funnel spout. If we find that asking “Why” one more time causes our “funnel” to widen out again, we are probably going beyond the root cause.
The 5 Whys is a systematic, logical approach to solving a problem by arriving at the true root cause – digging deep beyond the “symptoms” level to one where our countermeasure will eliminate the problem. As with anything, arriving at the right depth requires that your analysis be sound.