5 Whys


5 Whys is commonly listed more as a Lean tool than Six Sigma because it isn’t rigorously data-based, but it can be particularly useful, especially to Belts who get trapped in the minutiae and don’t step back to see the bigger picture (see “Other Options”). The simple idea is to keep asking “Why” (usually five times) to ensure that the root cause(s) of the effects are fully understood. The reasoning is that the result of each time the Why is asked gives a different answer, in essence peeling back the layers.

  • FirstWhy—Symptom
  • SecondWhy—Excuse
  • ThirdWhy—Blame
  • FourthWhy—Cause
  • Fifth Why—Root cause

A simple fictitious example demonstrates use of the tool well. A problem in London’s Trafalgar Square is that Nelson’s Column requires frequent, expensive repairs.2

2. The original source of this example is unknown. The example appears in various guises related to many national landmarks in Europe and the United States.

 First Why—Why does the column need frequent, expensive repairs? Answer—Frequent washing is damaging the stone.

Obvious solutions in this case include investing in less-abrasive cleaning mechanisms and perhaps different detergents. However, this still doesn’t reduce the frequency of washing.

Second Why—Why does it need to be washed so much?

Answer—There is a buildup of pigeon droppings.

Pigeons are a popular sight in Trafalgar Square, and obvious solutions in this case might include investing in a pigeon-scaring device or placing devices to stop pigeons from landing on the column. Unfortunately pigeons are arguably part of the tourist attraction itself, so this could be difficult to implement.

Third Why—Why are the pigeons gathering on top of the column?

Answer—The pigeons eat the spiders on the column.

Obvious solutions might include spraying the column regularly with pesticide to kill the spiders. The use of pesticides is frowned upon at the best of times in a highly pop- ulated area, but on such a visible landmark there could be major opposition. Also, the impact of the pesticide on the stone itself would have to be examined.

Fourth Why—Why are there spiders on the column?

Answer: The spiders eat the insects on the column.

The solution to the third Why still seems to work. The pesticide would kill both the spiders and the insects.

Fifth Why—Why are the insects there?

Answer—They are attracted to the brightly lit surface in the evening.

Proposed solution—Delay turning on the lights for 30 minutes and they will be attracted elsewhere.

Blog post extracted from the book Lean Sigma – A Practitioners Guide source – Ian Wedgwood, Ph.D., (2016) Lean Sigma – A Practitioners Guide, Prentice Hall

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