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Root Cause Analysis Using Five Whys

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Root Cause Analysis Using Five Whys

What is it and how can it help me?

By repeatedly asking the question ‘why?' (use five as a rule of thumb), you can peel away the layers of an issue, just like the layers of an onion, which can lead you to the root cause of a problem. The reason for a problem can often lead into another question; you may need to ask the question fewer or more than five times before you get to the origin of a problem.

The real key is to avoid assumptions and logic traps and encourage the team to keep drilling down to the real root cause.

When does it work best?

By quickly identifying the source of an issue or problem, you can focus resources in the correct areas and ensure that you are tackling the true cause of the issue, not just its symptoms.


How to use it

How to complete the five whys

  1. Write down the specific problem. Writing it down helps you formalise the problem and describe it accurately. It also helps a team focus on the same problem
  2. Use brainstorming to ask why the problem occurs then, write the answer down below
  3. If this answer doesn't identify the source of the problem, ask ‘why?' again and write that answer down
  4. Loop back to step three until the team agrees that they have identified the problem's root cause. Again, this may take fewer or more than five ‘whys?'

Why use the five whys?

  • Helps you to identify the root causes of a problem
  • Helps you to determine the relationship between different root causes of a problem
  • It is one of the simplest analysis tools as it's easy to complete without statistical analysis
  • It is easy to learn and apply

Five whys and cause and effect diagrams

The five whys can be used independently or as a part of a cause and effect diagram. The diagram helps you explore all potential or real causes which result in a failure or problem. Once you have established all the inputs on the cause and effect diagram, you can use the five whys technique to drill down to the root causes.


  • Moving into 'fix-it' mode too quickly might mean dealing with symptoms but leaving the problem unresolved, so use the five whys to ensure that the cause of the problem is being addressed
  • If you don't ask the right questions, you don't get the right answers. A question asked in the right way often points to its own answer 

Example 1
The patient was late in theatre, it caused a delay. Why?
There was a long wait for a trolley. Why?
A replacement trolley had to be found. Why?
The original trolley's safety rail was worn and had eventually broken. Why?
It had not been regularly checked for wear. Why?

The root cause - there is no equipment maintenance schedule. Setting up a proper maintenance schedule helps ensure that patients should never again be late due to faulty equipment. This reduces delays and improves flow. If you simply repair the trolley or do a one-off safety rail check, the problem may happen again sometime in the future.

Example 2

The patient's diagnosis of skin cancer was considerably delayed. Why?

The excision biopsy report was not seen by the surgeonWhy?

The report was filed in the patient's notes without being seen by the surgeon. Why?

It was the receptionist job to do the filing. Why?

The junior doctors were busy with other tasks. Why?


The root cause - that the doctors' other tasks were seen as more important than filing. The system has now  been changed. A copy of all biopsy reports is now sent to the consultant surgeon responsible for the patient and no reports are filed unless they have been signed by a doctor.


What next?

You may find that you will identify the root cause of the issue identified. The next suggested step is to complete a cause and effect diagram.

Brainstorming to help you to identify potential solutions to the cause identified. 

You will need to communicate the outcomes to others to ensure that the root cause of the problem is understood and that everyone is focused on working on the correct problem area, not treating its symptoms.

Additional resources

The five whys is a Lean tool now used in other areas so the following may be useful.


‘The New Lean Toolbox' (p152) John Bicheno, Picsie Books 2006

‘The Toyota Field Book' Jeff Liker, 2004



CHAIN's lean subgroup.

You will need to join via the webpage.  Most people in healthcare improvement are in CHAIN3. If you want to join, e-mail the CHAIN administrator at


Lean social bookmarks (login name: chaingroup; password: lean).  On the top left corner of the screen click on group ‘Lean thinking in healthcare'. 


NHS Networks -Lean Thinking


LEA's Lean Healthcare Network (this meets quarterly).

Institute's website: see service transformation


Bill Wilson Article



The five whys originated within Toyota as they developed their manufacturing

methodologies. It forms a critical component of their problem solving training and is part of the induction into the Toyota production system. It is now also used within Six Sigma.


Very often, the answer to the first ‘why?' will prompt another ‘why?' The answer to the second ‘why?' will then prompt another and so on; hence the name, the five whys strategy.


Acknowledgements / sources

Six Sigma - Determining the Root Cause: 5 Whys


The Improvement Network 


© Copyright NHS Institute for Innovation and Improvement 2008