Out like Flynn
<p>Renowned pychometrician Charles Murray has given us, in <a href="http://www.commentarymagazine.com/production/files/murray0905.html">The<br />
Inequality Taboo</a>, a concise summary of the most current science on<br />
group differences in IQ and other measures of capability.  Most of it<br />
is not surprising to anybody who has been following the actual science<br />
rather than press accounts severely distorted by the demands of<br />
political correctness.</p>
<p>There is some new information here, however, and perhaps the most<br />
interesting bit is that turns out to be much less to the Flynn effect<br />
than meets the eye.  The Flynn effect is the long-term rise in average<br />
IQ scores recorded since IQ began to be measured in the early 20th<br />
century.  Advocates of the view that IQ is unimportant or meaningless<br />
have seized on the Flynn effect to argue that IQ is either (a) a<br />
statistical artifact, or (b) almost entirely environmentally driven<br />
(and thus can presumptively be increased by correct social<br />
policy).</p>
<p>Murray&#8217;s news is that the Flynn effect is not being driven by a<br />
rise in average g, the measure of general mental ability that accounts<br />
for over 50% of variance in almost all kinds of mental aptitude tests.<br />
Since Spearman discovered the &#8216;g&#8217; statistic, almost all psychometricians<br />
have accepted that IQ is interesting precisely because it is a good<br />
approxmation of g.  Thus, the Flynn effect is basically a mirage &mdash;<br />
it&#8217;s taking place in the noise, not the signal.</p>
<p>I&#8217;m not entirely sure what this means yet, and I don&#8217;t believe<br />
Murray or other psychometricians have gotten to the bottom of it<br />
either.  But at minimum, it&#8217;s very suggestive that IQ differences are<br />
either genetic or driven by environmental factors over which we have<br />
little control.  Spearman&#8217;s g, in particular, is notoriously<br />
intractable.  It is highly heritable according to separated-twin<br />
studies. And while there is good evidence that it can be lowered from<br />
its &#8216;natural&#8217; genetic level by unfavorable environment (such as poor<br />
childhood nutrition), it apparently can&#8217;t be raised by a favorable<br />
one.</p>
<p>Indeed, Murray reports in a footnote evidence from a study in<br />
Denmark that the Flynn effect has leveled off since the early 1990s.<br />
Thus, it may be that we have already maxed out the effects of wealth<br />
and better nutrition on the both the g and non-g components of IQ that<br />
we <em>can</em> manipulate.</p>
