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Problem Definition Tools
There are numerous tools to assist the Lean Six Sigma team in the creation of the problem statement. Different tools work better in different applications, but all of them help the Lean Six Sigma team focus on the root cause problems and not chase symptoms.
When to use
The problem definition techniques are used during the Measure phase to develop the problem statement and assist in root cause identification.
The four techniques listed below are excellent in a team brainstorming environment. They are all easy to understand and easy to apply, yet can quickly lead to very valuable insights concerning the problem and the potential root causes. I normally use several techniques, selecting them based on the nature of the problem and the team I am working with.
Cause and Effect Diagram
This is a graphical technique that shows all the root cause categories that may be contributing to a problem. The high level problem is placed at one end of a horizontal line. The categories are drawn as branches off the horizontal line. Sub-categories are drawn as branches from the category lines. This technique can be used to track which categories and sub-categories have been measured and the results of that measurement. This technique is also known as the Fishbone diagram and the Ishikawa diagram.
The six M’s are a mnemonic for six potential categories of root causes; each category begins with the letter M. I often use these six categories for my major branches on a cause and effect diagram. This technique helps a team look for all potential root causes and not jump on the first likely cause they find while overlooking others that are significant. The six M’s are: Materials, Manpower, Machines, Methods, Measurements, and Mother Nature.
The Why technique is used to move from symptoms to root causes. It's as simple as asking Why multiple times. The technique assumes that there is an underlying cause for each problem symptom. That underlying cause had its own underlying cause. It normally takes anywhere from four to eight Why questions to reach a root cause. This technique is very helpful when trying to understand an unexpected problem.
Is / Is Not
This technique is a series of declarative statements about the problem. First, a statement about something that is associated or related to the problem followed by something that is not associated or related to the problem. After the first statement is made, an additional statement is added to further explain something associated with the occurrence of the problem and the Is Not statement is expanded to further clarify what is not associated. This continues for several more statements until there is a clear boundary between when or how the problem occurs and when it does not. This technique is very useful with inconsistent or intermittent problems.
Hints & tips
- Use multiple techniques. If one is helping your team gain understanding about the problem, move on to the next technique.
- The techniques often work best when someone is acting as a facilitator. This is a good time for your Black Belt to assist the team.
- Save the results of your analysis using these tools, they are great reference points if the team gets stuck in the Analyze phase.
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