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Date: Wed, 6 Oct 1999 01:36:49 -0700
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From: sarich@SSCL.Berkeley.EDU (Vincent Sarich)
Subject: [h-bd] African IQs
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Phil Rushton wrote:


<<Neither will "motivation" affect those 5 cubic inches of brain tissue
which underlies the test score differences. Black-white differences in
brain size have been known since long before Charles Darwin, who cited
them to help support his then controversial theory of human evolution
(1871). has anything ever been so known to science for so long and yet
so studiously avoided for political and wishful thinking reasons?>>


Those "5 cubic inches" are not nearly enough to underlie most of the test
score differences. 5 cubic inches equals about 80cc, which is substantially
less than one standard deviation. The correlation between IQ and brain size
is about 0.4, and the standard deviation of IQ is 15. Two populations that
differed in mean brain size by one standard deviation (about 130cc) would
then, everything else being equal, differ in mean IQ by 0.4 of a standard
deviation, or 6 points. An 80cc difference would thus be worth about 4
points; thus brain size differences as such could only account for a small
proportion of the black-white difference in IQ (whether they account for
any of it is of course another matter entirely).


Vincent Sarich






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