Re: MA MCAS statistical fallacy

[Paul R Swank]

Robert:

Why would you expect a strong correlation here? You're talking about tests done a year apart with some new kids in each school and some kids who have moved on.
Is regression toward the mean causing all of the noted results. Probably not. But it is quite conceivable that it could be partially responsible for the results.

At 03:21 PM 1/11/01 -0400, you wrote:
>
>
>Paul R Swank wrote:
>>
>> Regression toward the mean occurs when the pretest is used to form the groups, which it appears is the case here.
>
> Of course it "occurs": - but remember that the magnitude depends on
>r^2. In the case where there is strong correlation between the pretest
>and the posttest, we do not expect regression to the mean to be
>particularly significant.
>
> Now, it is generally acknowledged that there are some schools which
>_consistently_ perform better than others. (If that were not the case,
>nobody would be much surprised by any one school failing to meet its
>goal!) Year-over-year variation for one school is presumably much less
>than between-school variation.
>
> Therefore, I would not expect regression to the mean to be sufficient
>to explain the observed outcome (in which "practically no" top schools
>met expectations); and I conclude that the goals may well have been
>otherwise unreasonable. Indeed, requiring every school to improve its
>average by at least two points every year is not maintainable in the
>long run, and only justifiable in the short term if there is reason to
>believe that *all* schools are underperforming.
>
> -Robert Dawson
>
>
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------------------------------------
Paul R. Swank, PhD.
Professor & Advanced Quantitative Methodologist
UT-Houston School of Nursing
Center for Nursing Research
Phone (713)500-2031
Fax (713) 500-2033

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