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Eugene Stern: How Value Added Models are Like Turds

May 22, 2017

I didn’t get a chance to react to this on my own blog… and I’m glad I didn’t because this is not only a better explanation of the flaws in Dr. Sanders methodology but also offers a more pungent alternative to using standardized achievement test scores!


This is a guest post by Eugene Stern, originally posted on his blog sensemadehere.wordpress.com.

“Why am I surrounded by statistical illiterates?” — Roger Mexico in Gravity’s Rainbow

Oops, they did it again. This weekend, the New York Times put out this profile of William Sanders, the originator of evaluating teachers using value-added models based on student standardized test results. It is statistically illiterate, uses math to mislead and intimidate, and is utterly infuriating.

Here’s the worst part:

When he began calculating value-added scores en masse, he immediately saw that the ratings fell into a “normal” distribution, or bell curve. A small number of teachers had unusually bad results, a small number had unusually good results, and most were somewhere in the middle.

And later:

Up until his death, Mr. Sanders never tired of pointing out that none of the critiques refuted the central insight of the value-added bell…

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