Aging & Investing
To the Editor:
In the article “Aging & Investing: The Risk of Cognitive Impairment” (September 2011 AAII Journal), when David Laibson says that “Fluid intelligence would be the kind of intelligence used to solve a typical IQ question,” he implies incorrectly that IQ tests measure only fluid intelligence. The Wechsler Adult Intelligence Scale, the most widely used IQ test administered by psychometricians and psychologists, assesses at least as much crystallized as fluid intelligence, including subtests of Information and Vocabulary. Indeed, the Vocabulary subtest correlates most highly with the full-scale IQ.
Another point is that statistical relations that pertain to the entire population, which David Laibson discusses, cannot be generalized to members of AAII, who are a highly selected, non-random subset of the population, whose average level of education (and, almost certainly, average IQ) substantially exceed those of the general population. Only a small minority of the general population suffers mild cognitive impairment MCI and even fewer of the more educated.
To recommend actions to be taken by an individual based on group means is always illegitimate, but the error is greatly magnified when the individual comes from a highly selected subset of the population that is not even described b
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