In my last post, I told you how I had double-checked the analysis in a post that involved running the Johnson transformation on a set of data before doing normal capability analysis on it. A reader asked why the transformation didn’t work on the data when you applied it outside of the capability analysis.

I hadn’t tried transforming the data that way, but if the transformation worked when performed as part of the capability analysis, it should work when applied outside of that analysis, too.

But the reader was correct. The transformation failed when applied by itself.

What happened?

When I’d performed the capability analysis with the Johnson transformation option selected, the analysis seemed fine to me. It had been a while since I’d done a capability analysis, but the graph looked OK.

Then I remembered what one of my first Minitab instructors told me: “Always look at the session window.” So I did. And there it was:

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