What is Is/Is Not analysis?
Is/Is Not analysis is a structured way to describe a problem by contrast. Instead of only recording where a problem occurs, you also record where it could reasonably occur but does not. If leaks appear on PH-200 housings but not on PH-300 housings built on the same line, whatever differs between the two is a strong clue.
The technique is the core of Kepner-Tregoe problem analysis and is the recommended tool for D2 of the 8D method. It is especially powerful for problems that appeared suddenly where something must have changed.
The four dimensions
| Dimension | Typical questions |
|---|---|
| What | What object has the problem? What exactly is the defect? |
| Where | Where is the object when the problem is seen (site, line, region)? Where on the object is the defect? |
| When | When was it first seen? When since then, and is there a pattern? When in the process or life cycle? |
| Extent | How many objects are affected? How big is each defect? Is it increasing, stable or decreasing? |
Some teams add a fifth dimension, Who (who is involved, who detected it). Use it carefully: the goal is to find process differences, not to blame people.
From distinctions and changes to causes
- Distinctions: for each IS / IS NOT pair, ask what is unique, different or peculiar about the IS.
- Changes: for each distinction, ask what has changed in, on, around or about it, and when.
- Possible causes: ask how each change could have produced the problem.
- Test: check each possible cause against every IS and IS NOT. If it doesn't explain a fact, it is eliminated or needs an assumption.
Is/Is Not narrows the search; it does not replace verification. Confirm the most probable cause with data, a test or by switching the problem on and off. For broader brainstorming, start with a fishbone diagram, and if the key clue is a change, continue with a change analysis.
Is/Is Not example
The example investigates field leaks on PH-200 pump housings. Leaks appear only on PH-200 (not PH-300), only at the flange O-ring, only in hot climates, only on units built from week 18 and only after weeks of service. Two changes stand out: a new O-ring supplier from week 18 and a new bolt torque sequence from week 17. Testing the causes, the O-ring compound explains every fact, while the torque sequence needs an assumption (that the hot-climate pattern is a coincidence). The O-ring becomes the most probable cause, to be verified by a high-temperature compression set test.
Tips
- Make the IS NOT as close as possible to the IS. "Not on PH-300 built on the same line" is far more useful than "not on cars".
- Use facts, not opinions. Mark unknowns and go get the data.
- Watch the timeline. Changes just before the first occurrence are prime suspects.
- Keep eliminated causes in the record. They show the investigation was thorough.
How to use this Is/Is Not Analysis tool
- Write the problem as object + defect. Start with a concise statement naming the object and the deviation, such as "PH-200 housings leak at the main flange".
- Describe the IS. For each question under What, Where, When and Extent, record the facts about where the problem is observed.
- Describe the IS NOT. For each IS, record the closest place, time, object or extent where the problem could be but is not. This is the key to the method.
- Find distinctions and changes. Note what is unique about each IS compared to its IS NOT, and what changed in or around that distinction and when.
- Test possible causes. List causes suggested by the changes and test each one against all IS and IS NOT facts. Eliminate those that do not fit.
- Verify and export. Verify the most probable cause with data, then export the analysis for your 8D, CAPA or investigation report.
Frequently asked questions
What is an Is/Is Not analysis?
Is/Is Not analysis is a problem definition technique that describes a problem along four dimensions (what, where, when and extent) by stating where the problem IS observed and where it could logically be but IS NOT. The contrast narrows down the possible causes. It comes from the Kepner-Tregoe problem analysis method.
Where is Is/Is Not used in 8D?
In an 8D report, Is/Is Not is the standard tool for D2, Describe the Problem. It produces a precise problem description, and in D4 the possible root causes are tested against it.
What are distinctions and changes?
A distinction is something that is true of the IS but not of the IS NOT, for example "only units with the new O-ring". A change is anything that changed in or around a distinction, for example "O-ring supplier changed in week 18". Causes are usually found in changes affecting distinctions.
How do you test possible causes?
For each possible cause, ask: if this were the cause, would it explain every IS and every IS NOT? A cause that contradicts any fact is eliminated. The most probable cause explains all facts with the fewest assumptions. It must then be verified with data or a test.
Who invented Is/Is Not analysis?
Charles Kepner and Benjamin Tregoe developed the approach in the 1950s and 1960s as part of their rational process for problem analysis. It was later adopted in the Ford 8D methodology and in many automotive, aerospace and life sciences quality systems.
Can I export my Is/Is Not analysis?
Yes. Export it as a PDF report, a PNG image of the tables, an Excel workbook or CSV, or save a .json file to reopen and update later. The tool is free and your data stays in your browser.