Root Cause Analysis: 5 Why in problem solving

The key to effective problem solving is root cause analysis, or separating the symptoms from the cause, to identify what’s really causing the problem. You can then apply, validate and embed your countermeasures in the knowledge that it will eliminate the problem.

Ask why the problem occurred, then continue to ask why that happened
(5 times as a rule of thumb) until you separate the symptoms from the cause.

“Asking questions is the ABC of analysis”.

The method of 5Why analysis initially developed by Sakichi Toyoda in the 1930’s was later adopted by Taiichi Ohno and Shigeo Shingo and included in the Toyota Production System (TPS) they were developing, from where it has become a powerful and widely used analysis / problem solving tool.

5Why analysis is “The basis of Toyota’s scientific approach, by repeating why 5 times, the nature of the problem as well as its solution becomesclear.” Taiichi Ohno

When analysing a problem there are two root causes to be identified
1. Why the defect was made
2. Why the defect was not detected (at the point of cause)
the 5Why process, but more importantly, the ‘thinking way’ is an effective yet simple and flexible method to deliver robust results and help ensure that you resolve problems quickly and effectively.

Example: why the defect occurred


Example: why the defect wasn’t detected

Example Countermeasures
1. Specification for plug fuses developed, issued and communicated
2. Process for the replacement and verification of plug fuses developed, issued and communicated
3. Procedure for water temperature verification developed, issued and communicated

The advantages of the 5Why process;
Simple – It’s easy to use.
Effective – It quickly separates symptoms from the cause.
Comprehensive – It determines the relationships between various causes.
Flexible – It works well stand alone, but also when combined with other tools.
Engaging – By its nature it fosters and produces teamwork.
Inexpensive – It’s a team focused exercise so there are no additional costs.

How to ensure your 5Why’s work

  1. Use a cross functional team.
  2. Develop a simple process to follow, and stick to it (including a simple 5Why sheet or common format)
  3. Avoid assumptions
    Your 5Why is only as robust as the information it’s based on, so don’t assume anything, check everything.
  4. Visualise the information and data you use (7 Quality Control Tools)
  5. Test the logic
    You’re looking for an unbroken chain of logical links, think of it like a series of stepping stones across of river, no leaps of faith allowed.
    Tip 1: Say it out loud; it will sound wrong if it’s not logical
    Tip 2: Read it backwards as a series of ‘therefore’ (i.e. from Root cause back through the symptoms to the problem)
    Tip 3: Get someone independent to read it to you
  6. Validate the contents
    Is there any proof? – something you can measure or observe
    Is there any history? – evidence that this potential cause can produce this problem
    Is there anything underneath or behind this possible root cause?
    Are there any other causes that could create this problem?

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