Identify root cause (2) – 5 Whys

Hello everyone. Last time, I wrote about “Fishbone Analysis”, one of the methods used in the “Analyze” phase, which we can say is the “internal research” stage of Lean Six Sigma.

This time, I would like to write about another technique used in this “Analyze” phase: the “5 whys”.

1. What is “5 Whys”?

The “5 Whys” originated from the origin of Lean, the Toyota Production System. It is also written in the book “Toyota Production System” by Mr. Taiichi Ohno, who is said to be the “Father of the Toyota Production System”.

As the name suggests, for specific issues, we ask “Why are these issues happening”? And in the above “Toyota Production System”, it is said to repeat why five times, so it is known as “5 whys”.

There is a famous example of “5 Whys”, so please watch this video (about 1 min 30 seconds).

Video1. “5 Whys” Jefferson Memorial (ASQ TV)

The flow can be simplified as follows.

Issue: The walls of the memorial were deteriorating.

Why 1: Why the walls were deteriorating?
-> Because they had to use high pressure cleaners every 2 weeks.

Why 2: Why they had to use high pressure cleaners every 2 weeks?
-> Because of so many bird droppings.

Why 3: Why were there so many birds?
-> Because birds were eating spiders at the memorial.

Why 4: Why were there so many spiders?
-> Because they were eating insects at the memorial.

Why 5: Why were there so many insects?
-> Insects came to the memorial when it’s lit up at night.

Break down the issue like this. In this case, by taking the last factor into account, the issue was solved by turning off the light at night, and as a by-product, by turning off the light, the electricity cost was also reduced. What a beautiful case!

2. Key points for “5 Whys”

I personally think that there are 2 key points in “5 Whys”.

Point 1 – Stop at a depth where you can think of realistic solutions

It is difficult to know when to stop this deep-diving, but it is something like “every time you find a cause, discuss a solution and whether it’s realistic”.

For example, in the above Jefferson Memorial case, if the solution to the first factor, “The condition is deteriorating due to the effects of high-pressure cleaner every two weeks”, is to “reduce the number of high-pressure cleans”, then it may slow down the deterioration of the wall. But it may also increase the damage of bird droppings and it will not be a fundamental solution, right?

Conversely, too much deep-dive is also no good. For example, in the above example, in response to the 5th factor, “Insects came to the light at night”, if we further break down into “Why do insects come to the light at night?”, and if we find the answer like “because it’s a habit”, I don’t think there’s anything we can do about it. We might come up with the idea of changing behavior through genetic manipulation (laughs), but that’s not realistic.

It is difficult to say for sure, but I think we have no choice but to give it a try. One thing I can say is that you don’t have to stick to “5 times”. It doesn’t matter how many times as long as you find a realistic solution.

Point 2 – Prudent facilitation is important

In the Jefferson Memorial video above, the “why” is repeated and the causes are explored quite smoothly, but in reality it doesn’t work so well:) In that case as well, I guess that there were various discussions along the way and that was the summarized results.

It may be especially true for Japanese people that if we repeatedly ask “why?”, then it sounds like interrogation and it would be painful. So facilitation skills to prudently identify them are important (I would like to write about facilitation later in this blog).

Here are some facilitation ideas;

Idea 1 – Utilize “Silent brainstorming”

Distribute post-its to the discussion participants and ask them to write down the reasons for the question of “Why?” Once you have finished writing, you can share it and discuss which one is better. I think we can reduce the sense of “interrogation” by repeating this.

Idea 2 – Utilize “Self brainstorming”

This is a variation of Idea 1, but at first, ask each member to individually breakdown from the first issue to the root cause, then bring them together and discusses which is better.

These are just a few examples, but I think it would be good if you could actually try them out and find a way that is easy for you to do.

3. Cross-analysis of “Fishbone” and “5 whys” – but isn’t that a “Logic tree” after all? !

It is also effective to cross-analyze (combine) this “5 Whys” and “Fishbone analysis” posted last time. Here is the image of cross-analysis.

Cross-analysis of Fishbone and 5 Whys (Image)
Fig1. Cross-analysis of Fishbone and 5 Whys (Image) Source: ROBOT Befriend

From the image of the fishbone posted last time, the cause of “Manual is not up to date” on the bottom right is explored with “5 Whys”. By using it together like this, you can deep-dive to the appropriate depth without missing the cause of the issue.

Here, if you have a good intuition, you may think, “But isn’t that a logic tree after all”? You are correct in fact.

Added 5 Whys to the logic tree (Image)
Fig2. Added 5 Whys to the logic tree (Image)

This is also the image of the logic tree posted last time, with the elements in Fig1 above added. It’s logic tree itself, isn’t it?

This point is the same conclusion as last time, but I think that there are preferences, so I think it’s good to use the one that is easy to use and fits perfectly!

That’s all for this time, and I would like to continue from the next time onwards. Thank you for reading until the end.

Sponsored Link