Aging and IQ
Gwern Branwen
http://www.huffingtonpost.com/scott-barry-kaufman/intelligence-is-still-not_b_1078112.html
> In 1932, the entire population of Scottish 11-year-olds (87, 498 children) took an IQ test. Over 60 years later, psychologists Ian Deary and Lawrence Whalley tracked down about 500 of them and gave them the same test to take again.
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> Turns out, the correlation was strikingly high -- .66, to be exact. Those who were at the top of the pack at age 11 also tended to be at the top of the pack at age 80, and those who were at the bottom also tended to stay at the bottom. Equally as interesting, the correlation was far from perfect. A few outliers could be found. One person had an IQ of over 100 at age 11, but scored just over 60 at age 80. There are many possible reasons for this outlier, including dementia. Other folks showed IQ increases as they aged. On average, people's individual (or absolute) scores on the test taken again at age 80 was much higher (over one standard deviation) than their scores had been at age 11, even though the rank ordering among people stayed roughly the same.
I am guessing the cases where IQ increased were far less dramatic than
the cases where it decreased... A reminder, for all of us, of one the
basic principles we should remember in evaluating interventions: IQ is
much easier to decrease than to increase.
> One study (http://www.fed.cuhk.edu.hk/%7Elchang/material/Evolutionary/IQ%20and%20cortical%20thickness.pdf) followed 300 children up to early adulthood. At age 7, the higher IQ children (greater than 120) tended to have less cortical thickness. Soon after, however, the high IQ children showed a rapid increase in cortical thickness, overtaking the other children and peaking at age 11-12 before slowly declining to about the same level as the others. The researchers concluded
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>> "'Brainy' children are not cleverer solely by virtue of having more or less grey matter at any one age. Rather, intelligence is related to dynamic properties of cortical maturation."
re the teenager study we discussed recently:
> It was a small sample, it's not clear that the tests they administered were age-appropriate for all of their participants, and some of the high-IQ children tested at the first time point may have found the test too easy (showing 'ceiling effects'). Future research should look at larger samples, using a number of different tests, on a wider range of ages. It remains to be seen if the same levels of plasticity are evident among older populations.
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> At any rate, it's a neat little study and contrary to an article in the Guardian, which stated that the study "contradicts a long-standing view of intelligence as fixed", the study is actually quite consistent with what IQ researchers have been finding for over 50 years! No sensible IQ researcher would say that intelligence is fixed. Anyone who does tell you that is a nut job.
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gwern
http://www.gwern.net