Nice bit of stats there, but in general, IQ scales still have a
mean of 100 and a standard deviation of 15. Without going and
measuring the Bell curve, the corresponding figures work out to
produce a similar net effect of the 80-120 calculation.
What IS important about an SD of 15 lies in the definition of a SD.
Put simply, if you have two people who are one SD apart from each
other, you really don't need any measurement instrument to notice
the difference.
The key aspect of IQ has also been missed out here, namely what it
means. The formula for calculating IQ is (Mental Age/Chronological
Age) X 100, which works out effectively into a percentage, e.g. an
IQ of 125 states that you have the intellectualy ability expected
of an average person who's 125% of your age.
Also, there's little point in talking about IQs of over 160. The
sample of the population represented is so small that no score
above that can be considered statistically sound.
While the passages you cited are all right as a general reference,
I would take them with a pinch of salt. IQ tests, unfortunately,
are subject to bias, be it in the form of gender, language or
education. For example, you could have someone who's pretty
intelligent from say, the Australian outback, but who would not be
able to perform on any tests of common Western knowledge. Research
indicates that men have the advantage over women in terms of
visuospatial abilities, so tests involving things like rotating
figures would be biased in favour of men. So on and so forth. Fact
of the matter is that the only thing that the result tells you is
how well you did on the test. Theoretically, the ideal measure of
intelligence would be Spearman's g, but in a century nobody's been able
to define it properly in an operational sense, much less test it.
At the end of the day, you could have someone with an IQ of 145 and
he could still be dumb as dogsh*t in a practical sense.
When it comes to measurement of intelligence (or to be politically
correct, intellectual ability), the instruments currently being
used are far from perfect. Over and above the bias issues described
above, you've also got a problem with assessing the difficulty of
the test. Traditional test theory is based on a vicious cycle: the
worse people do on a test, the harder it is, but the less able the
people are, the worse they do. The question this system fails to
answer is: are the people less able or is the test harder? Recent
developments in Item Response Theory have started to address this
issue, but it'll be a while yet before we get a system that
comprehensively replaces the current system.
The last time I head, Mensa requires a verified IQ score of 145 for
membership (I believe it was raised from 135 about a decade
ago).
As to what's considered a high IQ, it's a subjective matter. let's
face it, if you've got an IQ of 101, you're smarter than the
average bear already. As a rule of thumb, if you're over 120,
you're doing all right.
From a clinical perspective, I'd choose the Weschler Adult
Intelligence Scale (WAIS) as a measure of intellectual ability to
produce an IQ score. However, if I did want to work out how quick
someone is intellectually, I'd use Raven's Standard and Advanced
Pattern Matrices.
