DLyons Nov 1, 2015:

Here's a final example of a Flächentransformation - in this case a "t-score transformation" : "Wenn die Rohwerte nicht normal verteilt sind, kann man die übliche z-Formel nicht anwenden. Eine Möglichkeit der Anpassung an die Normalverteilung ist die Flächentransformation (T-Wert-Normierung)."

Again, that doesn't apply to stanines!

To summarize what I've been saying. "Flächentransformation " might best translated generically a "normalization transformation". More specifically, in the field of testing it seems to be used for McCall's Area Transformation.
Neither these really apply to stanines which is what the ST seems to be talking about. So I find the ST rather surprising (and perhaps inaccurate on this point?)

It's oversimplistic of Wiki to say that Flächentransformation is the same thing as Normalrangtransformation, although they are closely related.

To coin a phrase "Context is all" and I don't have a definitive answer. I suggest you refer it back to the client.

DLyons Nov 1, 2015:

Area Transformations Attempt to get the same area underneath the score distribution curve as in a normal distribution. They change the unit of measurement and also the unit of reference. Here, it seems like we are dealing with stanines https://en.wikipedia.org/wiki/Stanine which use a rank transformation to a normal curve.

Flächentransformation: https://books.google.ie/books?id=--MdBgAAQBAJ&pg=PA75

Here's an English reference where "area transformation" is being used https://books.google.ie/books?id=lYf5G-Ju46EC&pg=PA122

So I think one needs to know exactly what the raw scores are being converted into. If into percentiles, then this is a nonlinear transformation and "area transformation" may be appropriate. If into stanines then this is a linear transformation and "area transformation" is inappropriate.

"Prozentrang-Normen sind auch bei nicht-normalen Verteilungen verwendbar, da sie nicht auf einer linearen, sondern einer Flächentransformation der Rohwerteverteilung basieren."

Susan Welsh (asker) Nov 1, 2015:

@gangels I'm the one who wrote that Flächentransformation and Normalrangtransformation are the same thing, based on the Wikipedia entry: https://de.wikipedia.org/wiki/Normalrangtransformation . Is this incorrect?