Herman Rubin wrote:
> This is not done that often, and is generally quite difficult.
> It requires changing the form of the model. The more typical
> transformations attempt to get normal marginals, and there is
> rarely justification for this. It has done harm; many of the
> newer IQ tests never return "profoundly gifted", as this is
> beyond the range which the "normal" transformation of the scores
> from the too-small sample yields.
This may not be a bad thing, as it is not clear that the tests are
designed to make accurate distinctions for that part of the range of
intellectual ability.
I am not an expert on IQ tests (or a particular believer in the utility
of what they measure), but from what I have seen of them, the maximum
possible score does not represent an extraordinarily high ability level.
Moreover, a score that falls moderately short of the maximum may result
from traits such as carelessness that are not what the test is trying to
measure, rather than from lack of ability - or even from giving a
logical but obscure answer to a question intended to be obvious.
We see this in other tests as well. One can probably say less about
the distinction in ability between students who get 95% and 100%
respectively on an exam than about that between students who get 70% and
75% respectively. Standard grading schemes tend to echo this, assigning
various flavors of A over a wider range than for B's or C's. Similarly,
a smart graduate committee will pay more attention to the recommendation
of a summer research supervisor or honors thesis advisor than to the
distinction between a GPA of 4.1 and one of 4.2.
Similarly, at the lower end, most standard adult IQ tests presumably do
not distinguish below a certain level at which the subject is incapable
of following the instructions.
Extremes of ability need to be measured with special instruments.
-Robert Dawson
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