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November 2009
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Why, oh why, oh why…

If your children keep asking “why?” over and over again it can become irritating quite quickly, often resulting in “because I say so!”.

You may be surprised to learn that, in the grown-up world, asking “why?” several times in succession is actually a valid technique for Root Cause Analysis, in other words, looking at a problem and working out what really caused it (as opposed to identifying a secondary or non-causal link with the problem which more superficial analysis can often do.)

Although its philosophy is quite old, the 5 Whys technique was made popular in Japan (and, arguably, by children the world over) and became an integral part of the famous Toyota Production System in the 1970s.

The technique involves taking a problem and asking “Why – what caused this problem?”. You then take the answer and then ask “Why – what caused that to happen?”. Then take the answer and again ask “Why – what caused that to happen?”. By repeatedly asking the question “Why” you can get to the bottom of the problem – its root cause.

5 is merely a typical number of Whys, by the way, and is not set in stone; you might get there in 3 Whys, it might take 8 or more.

Here’s a trivial example to illustrate the 5 Whys technique:

Problem – my laptop won’t turn on.

  1. Why won’t it turn on?
    Because the battery is dead.
  2. Why is the battery dead?
    Because the battery charger has not been charging it up.
  3. Why has the battery charger not charged it up?
    Because there is no mains power to the floor sockets in this part of the office.
  4. Why is there no power to the sockets?
    Because the mains circuit breaker tripped out this morning and hasn’t been reset.
  5. Why has the circuit breaker not been reset?
    Because we don’t have an agreed way of getting the off-site facilities people to come in and reset it, and no-one knew what to do.

So the root cause of the dead laptop is that the way that facilities support is provided in the company – no-one knew how to get the electricity turned back on. The corrective action could be to make sure everyone knows the right way to contact the on-call electrician, or maybe to train on-site staff to provide first-line support.

The benefits of the 5 Why technique are that it is simple and quick to get to the root cause, it can help you to work out the relationships between different root causes, and it is easy to use.

However, it is not without its critics.

The more complex the problem, and the more Whys you need to use, the more chance there is of it giving misleading results.

The people using it are limited by their own knowledge and may tend to stick with the symptoms of the problem rather than finding the real root cause. They will tend to find answers and root causes that are in their own comfort zone; if you ask a different group of people to run the 5 Whys process for a given problem they may come up with a different root cause. Also, it is easy to feel that you’ve finished when you have found an answer or root cause, but in practice there may be other contributing factors that you have overlooked.

A good discipline is to thoroughly test the result of each Why question – prove that each answer is valid and robust and there aren’t other factors at play before moving on to the next question.

5 Whys can be a useful tool but it shouldn’t be the only tool in your toolbox; ‘if all you have is a hammer, then every problem looks like a nail’! Use it when it’s appropriate to the problem in hand, don’t use it to solve everything.

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1 comment to Why, oh why, oh why…

  • Tom,

    I like your post on 5 Why’s. I’d be one of those critics of the tool. I have always struggled to get value form a 5 why’s exercise. My most frequent experience with this tool is that is leads you down a path you wish to go down. I’ve never been surprised by the outcome of a 5 why’s exercise. I find it to be of very limited value and have virtually eliminated it from my tool box.

    Jim Wells

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