SC QUALITY GUILDIs / Is Not problem specification
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Specify the problem on four dimensions, what it is and what it could be but is not. Find what is distinctive about the IS and what changed there, then test every possible cause: a true cause explains both sides.
ON THE EXAM · CMDA V.A, CQE V.E, CSSBB VI.D.2 · FREE · NOTHING YOU TYPE LEAVES YOUR BROWSER
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What the method does
Is / Is Not is the problem-analysis part of the Kepner-Tregoe method. Instead of brainstorming causes first, the team writes a precise specification of the problem, then uses it as a test that every proposed cause has to pass. It works best on a deviation that appeared at some point: something that used to be right and now is not.
Specify the problem
For each dimension, write what the problem IS and what it IS NOT but reasonably could be:
- What: which object has the defect, and what exactly the defect is.
- Where: where it is seen (line, site, customer) and where on the object.
- When: when it was first seen, the pattern since, and when in the life cycle.
- Extent: how many, how big, and the trend.
The IS NOT is the half that gives the method its power. "Line 1" alone suggests nothing. "Line 1, not line 2, which uses the same powder" rules out the powder at once. Pick the closest comparison: the thing most like the IS that does not have the problem.
Distinctions and changes
For each pair, ask what is distinctive about the IS: what is true of it and not of the IS NOT. Then ask what has changed in, on or around each distinction, and when. A problem that started on a date almost always follows a change, and the change is usually sitting next to a distinction.
Test the possible causes
Write each possible cause as a mechanism: how this change could produce this defect. Then test it against every row: if this is the cause, does it explain why the problem is here and not there? A cause that cannot explain an IS NOT is eliminated, however plausible it sounded. A cause that explains a row only if something else is true is kept, with that assumption written down.
The most probable cause is the one that explains the specification with the fewest and most reasonable assumptions. It is still a hypothesis: confirm it by checking the assumptions and by turning the cause on and off.
Is / Is Not, fishbone or 5 whys?
A fishbone generates many possible causes from experience; Is / Is Not narrows them with facts, and the two work well together. The 5 whys follows one chain of causes down. In an 8D, the Is / Is Not is usually part of D2, and its test of causes is part of D4.
On the exam
CMDA V.A lists Is/Is Not (Kepner-Tregoe) by name among the quality control and problem-solving tools. CQE V.E covers failure analysis and root cause analysis in corrective action, and CSSBB VI.D.2 covers the tools used to find root causes of chronic problems. Expect a scenario where you must say which possible cause is consistent with the facts, or which comparison (the IS NOT) is most useful.