On Tue, 2 Nov 1999, Susan Carmack wrote:

> >Another odd paradox is the fact that IQ scores have steadily and
> >substantially *risen*
>
> According to whom? "They" say we are living longer too, but many of my
> friends are dying with cancer and heart disease in their 40s and 50s....?

This is precisely why we do statistical studies -- to correct the
bias in our private observations of things.  That people are
living longer does not mean that your friends are not dying, and
it doesn't mean that they are healthier either.  It is well
understood that one important reason why people are living longer
is that tertiary medical intervention has improved so
dramatically.  My father had an aortic aneurysm 9 years ago that
would have killed him if it hadn't been for medical technology.
A month ago he had a quadruple bypass operation, at 75.  He may
well live into his 80s now, but it won't be because he is
healthier...

Anyway, concerning your question about IQ scores, the answer is
that the psychometricians who design and norm the tests have the
information.  IQ test are normed so that the average score for
the test population is 100.  It's not a raw score.  But the tests
have had to be-renormed several times since the 1930s, because
the raw scores are going up.  This means that a raw score that
would have meant an average IQ of 100 in, say, 1940 would give an
IQ score in the low 70s, the "mildly retarded" range, today.
Conversely, the raw score that give an IQ score of 100 today
would have corresponded to a "gifted" IQ in 1940.

Thus, in the case of IQ tests we have a very large paper trail to
support the claim that "intelligence", as measured by these
tests, is rising.  Strictly speaking, of course, IQ itself does
not change because the numbers are manipulated to make sure that
average is always 100.

Todd Moody
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