Human Intelligence and Medical Illness: Assessing the Flynn Effect (The Springer Series on Human Exceptionality)
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As critics will note, psychometric tests are deeply flawed. Person-to-person differences in performance on a psychometric test are not informative about many things of great interest. An intelligence quotient (IQ) cannot characterize creativity or w- dom or artistic ability or other forms of specialized knowledge. An IQ test is simply an effort to assess an aptitude for success in the modern world, and individual scores do a mediocre job of predicting individual successes. In the early days of psychology, tests of intelligence were cobbled together with little thought as to validity; instead, the socially powerful sought to validate their power and the prominent to rationalize their success. In recent years, we have ob- ated many of the objections to IQ that were so forcefully noted by Stephen Jay Gould in The Mismeasure of Man. Nevertheless, IQ tests are still flawed and those flaws are hereby acknowledged in principle. Yet, in the analysis that follows, individual IQ test scores are not used; rather, average IQ scores are employed. In many cases – though not all – an average IQ is calculated from a truly enormous sample of people. The most common circ- stance for such large-scale IQ testing is an effort to systematically sample all men of a certain age, to assess their suitability for service in the military. Yet, it is useful and prudent to retain some degree of skepticism about the ability of IQ tests to measure individual aptitudes.
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increase in white matter volume, such that there are rapid changes in the relative proportion of gray matter to white matter until about age 25 . Because the overall brain volume is stable by age 12 , this implies that any decrease in gray matter volume after age 12 must be offset by an increase in the volume of either white matter  or the cerebrospinal fluid around the brain. Whether the decrease in gray matter volume between age 20 and age 40 can be entirely explained by white matter