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5 Whys

Five Whys, sometimes written as “5 Whys,” is a guided team exercise for identifying the root cause of a problem. Five Whys is used in the “analyze” phase of the Six Sigma DMAIC (define, measure, analyze, improve, control) methodology.

The exercise begins with a facilitator stating a problem and then asking the question “Why?” (meaning “Why did the problem occur?”). The group brainstorms answers based on direct observation. Once the group agrees upon an answer, the facilitator again asks the question, “Why?”

The exercise got its name because it generally takes five iterations of the questioning process for the group to arrive at the root-cause of a problem -- but it is perfectly correct for the facilitator to ask less than five “whys” or more than five “whys” depending on the group’s needs.

Here is an example of how a Five Whys exercise might proceed:

Facilitator: Our websites were down from 2pm to 2:45 pm on Saturday. Why?

Group: Because the external DNS server failed.

Facilitator: Why did the external DNS server fail?

Group: Because the central process unit (CPU) was peaked at 100% and couldn’t handle outside requests.

Facilitator: Why did the CPU peak at 100%?

Group: Because the server kept trying to auto-update Windows.

Facilitator: Why did the server keep trying to auto-update Windows?

Group: Because when the administrator created the server, he forgot to uncheck the auto-update service.

Facilitator: Why did the administrator forget to uncheck the auto-update service when he created the server?

Group: Because he was in a hurry and got distracted by an alarm going off.

Once the team has agreed that they have identified the root cause of the problem – in this case, the administrator getting distracted and forgetting to turn off auto-update, the facilitator should help the group to determine corrective action.

Facilitator: How can we make sure that each administrator unchecks auto-update when he creates a new server, no matter how hurried or distracted he gets?

Group: Create a vanilla server image with auto-update turned off. Have administrators clone this image when deploying new servers.

Five Whys originated in the Toyota Production System, where it was used for post-mortem investigations into equipment failures and workplace safety incidents. It has proved to be especially useful for helping management teams identify and fix problems that at first glance appear to be technical problems, but upon further investigation, turn out to be people problems.

This was last updated in September 2012

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