Re: Statistics Question

[gerald bracey <gbracey@EROLS.COM>]

The distribution of the SAT is subject to fluctuations because of who takes
it.  A score of 200 is three standard deviations below the mean and that
accounts for 99.87 percent of the population.


----- Original Message -----
From: "Victor Steinbok" <Victor.Steinbok@VERIZON.NET>
To: <ARN-L@LISTS.CUA.EDU>
Sent: Monday, January 28, 2002 4:08 PM
Subject: Re: Statistics Question


> At 12:36 PM -0800 1/28/02, Ed Levine wrote:
> >To: ARN-L
> >
> >My statistical comprehension is apparently (based on NY State's
definition)
> >only a "2" (Does Not Meet Standard).  In an effort to understand what
> >"norm-referenced" means, I have a (perhaps naive) question.
> >
> >Don't the people who construct standardized, norm-referenced exams seek
to
> >atttain a bell-shaped curve when they norm the tests on a sample
> >group prior to
> >selling the test to the public?
> >
> >And, how is a rectangular (AKA "uniform") distribution possible if a test
is
> >"properly" normed?
> >
> >Thanks in advance to the person or persons who help me out of this
quandary.
>
> Gerry might have answered the question to your satisfaction already,
> but I'll take a crack. Distribution by percentile is ALWAYS uniform
> (rectangular), since the same number of students (in theory) classify
> for each percentile rank. The scores do not correspond to percentiles
> in the same fashion--they are stretched out at the top and bunched up
> in the middle, resulting in something resembling a bell-curve
> scenario.
>
> Incidentally, I am wondering if the bell-shaped distribution is
> expected for ALL norm-referenced tests. Certainly, SAT might be
> expected to be skewed toward the low end, as 200 does not represent
> the lowest scores, just a cut-off score for the lowest performing
> population. In other words, people who get a 0 a 3 or a 10 all get
> the same 200 score and the number of such people is sub-1%, unlike
> the scores at the top of the scale. Perhaps I am just interpreting
> the SAT scale in correctly.
>
>         VS-)
>
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