How to use the 5 WHY approach

Schema of the Process of problem solving. Base...

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The 5 WHY technique, developed by Sakichi Toyoda, is one of the core problem solving tools used by Toyota Motor Corporation and has been adopted and embraced by numerous companies all over the globe.  This technique is unconstrained, providing the team with a high degree of freedom in their thinking process.

As we suggested in our “How to Improve OEE” post, the 5 WHY system is simple in principle.  This simplicity may also be the downfall of this technique unless you take the time to understand and apply the process correctly.  Other problem solving tools, such as Cause and Effect diagrams, allow for the development of multiple solution threads, in turn creating the potential for multiple solutions.

Some root-cause analysis experts have correctly identified some of the short comings presented by the 5-WHY technique including:

  1. The approach is not repeatable – One problem, different teams, different solutions.
  2. The scope of the investigation is constrained by the experience of the team.
  3. The process is self directing based on the evolution of the “WHY + Answer” series.
  4. The TRUE Root Cause may never be identified – Symptoms may be confused for Root Causes.
  5. The inference that a root cause can be determined by a 5 tier “Why + Answer” series.
  6. The Problem Statement defines the Point of Entry. It is imperative to define where the real problem begins.

We would argue that any problem solving or root-cause analysis tool is subject to some short falls in one form or another.  Perhaps even in problem solving there is no definitive solution.  Different problems require different tools and perhaps even different approaches.  In the automotive industry, each customer has a different variation on the problem solving approach to be used and prescribe various tools to be used in the problem solving process.

For this reason, most companies do not rely on one single technique to approach their problem solving challenges.  We would also argue that most companies are typically well versed in their processes (equipment and machines), products, and applications.  As a result, having the right people on the team will minimize the experience concerns.  There is no reason not to include outside expertise in or outside of your current industry.

One concern that can be dismissed from the above list of short comings is the inference that the solution can be found by a 5 tier “Why + Answer” series.  There is no rule as to how many times the “Why + Answer” series should be executed.  Although five times is typical and recommended, some problems may require even deeper levels.  We recommend that you keep going until you have identified a root cause for the problem that when acted upon will prevent its recurrence.

The TRICK:

The technique that we propose in this post will at least provide a method to validate the logic used to arrive at the root cause.  Most 5-WHY posts, web sites, articles, or extracts on the topic seem to focus on a top-down or deductive “Why + Answer” logic sequence.  The challenge then is to have some way to check the “answer” to see if it actually fits.

A simple way to validate the top down logic is to read the analysis in reverse order, from the bottom up, substituting the question WHY with the words “Because” or “Therefore.”  To demonstrate the technique we’ll use an example based on a problem sequence presented in Wikipedia:

I am late for work (the problem):

  1. Why? – My car will not start. (The Real Problem)
  2. Why? – The battery is dead.
  3. Why? – The alternator is not working.
  4. Why? – The alternator belt is broken.
  5. Why? – The alternator belt was well beyond its useful service life and was never replaced.
  6. Why? – The car was not maintained according to the recommended service schedule. (Root Cause)

You probably noticed that we used a 6 “Why + Answer” series instead of 5.  We did this deliberately to demonstrate that 5 WHY is a guideline and not a rule.  Keep asking WHY until you find a definitive root cause to the problem.  We could keep going to determine why the car was not maintained and so on to eventually uncover some childhood fear of commitment but that is beyond the scope of our example.

The CROSS CHECK – Root Cause Analysis Validation

Root Cause: The car was not maintained according to the recommended service schedule.

  1. Therefore, the alternator belt was well beyond its useful service life and was never replaced.
  2. Therefore, the alternator belt is broken.
  3. Therefore, the alternator is not working.
  4. Therefore, the battery is dead.
  5. Therefore, the car will not start. (The Real Problem)
  6. Therefore, I will be late for work.

Does the reverse logic make sense to you?  It seems to fit.  Does it sound like the owner of the car needed to be a mechanic or at least know one?  When it comes to car trouble, we don’t seem too concerned about going to the outside experts (the mechanic) to get it fixed.  Why do some companies fail to recognize that experts also exist outside of their business as well?  In some cases, proprietary or intellectual knowledge would preclude calling in outside resources.  Barring that, some outside expertise can certainly bring a different perspective to the problem at hand.

Caution!  Stick to the Problem – Don’t Assign Blame

The original Wikipedia example identified the root cause as, “I have not been maintaining my car according to the recommended service schedule.”  It would be too easy for someone to say, “Aha, it’s entirely your fault.  If you only took better care of your things you wouldn’t have been in this predicament.”  For this reason, we presented the case based on the facts.  It’s not WHO it’s WHAT.  This approach also tempers emotions and keeps the team focused on the problem and the solution.

Where do we start? Problem Entry Points

You have likely noted that the problem statement is the key to establishing a starting point for the 5 WHY process.  A problem may have different entry points depending on what stage you become involved:

Entry Point Problem Statement
You Late For Work
Service Manager The car will not start
Mechanic The battery is dead
Belt Supplier The alternator belt is broken

Product Recalls and Warranty Returns are typical examples of where you may find multi-level 5 WHYs.  Ultimately the suppliers of most products, like the Belt Supplier in our example, will also complete a 5 WHY.  This is typically the case for most Tier I automotive suppliers.

WHY MAPS / TREES.

The one drawback or downfall of the 5 Why process as presented above and also used by most companies is the suggestion that a single “WHY + Answer” series will evolve into a neat single root cause.  Our experience suggests that this is far from reality.  We typically present the single series as part of the final solution, however, we can assure you that multiple root cause / solution threads were developed before arriving at the final result.

We use the WHY MAP (WHY TREE) as a tool that allows us to pursue multiple thought threads simultaneously.  Pursuing multiple threads also stimulates new ideas and potential causes.  In some cases the root cause analysis threads lead to the same or common root cause.  Then it is a matter of selecting the most likely root cause.

Tip:

Problem solving TREES come under many different names including Why-Tree, Cause Tree, Root Cause Tree, Causal Factor Tree, Why Staircase Tree, and Cause Map to name a few of them.  As you can see from the names, they all serve to create, stimulate, and propagate ideas.

Regardless of the tool you use, finding the true root cause and ultimately the solution to resolve it is the key to your problem solving success.

We trust this post will provide you with some insight to using the 5-WHY approach for problem solving and will serve as a useful tool to improve your OEE.

More on this series to follow in our next post.

Until Next Time – STAY lean!


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  1. Kelly
    April 26, 2011 at 2:17 am

    I just would like to give a huge thumbs up for the great info you have here on this post. I will be coming back for more.

  2. July 21, 2012 at 1:31 pm

    I would like to quote in a book your “6- Why’ approach can i use that with your permission and by giving your reference please?

    Shams Arifeen

    • July 21, 2012 at 4:09 pm

      It would be an honor! I will forward an e-mail granting permission to do so accordingly.

      Thank you for taking the time to visit our site.

      Redge

  1. March 18, 2010 at 9:44 pm

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