IQ has suddenly become a hot topic again, owing to a certain DNA-discovering Nobel laureate putting his foot in his mouth and the publication of a couple of books on the subject. Malcolm Gladwell has written a great article for the New Yorker that summarises many of the recent arguments and suggests why comparing IQ scores of different races is doomed to failure.
IQ is designed so it always has a mean of 100 and a standard deviation of 15. However, during the past decades people have been scoring better on IQ tests, something known as the Flynn effect, meaning the new versions have been re-adjusted to make sure the mean stays at 100.
This is important, because it means that comparing IQ from the 1950s is not a far comparison to IQs from the 2000s, because they use tests with different standards.
Some of the people who argued that certain races are more intelligent than others have failed to include these changes in their calculations, and, as Gladwell points out, when these are accounted for, many of these differences completely disappear.
The best way to understand why I.Q.s rise, Flynn argues, is to look at one of the most widely used I.Q. tests, the so-called WISC (for Wechsler Intelligence Scale for Children)…
For instance, Flynn shows what happens when we recognize that I.Q. is not a freestanding number but a value attached to a specific time and a specific test. When an I.Q. test is created, he reminds us, it is calibrated or ‚Äúnormed‚Äù so that the test-takers in the fiftieth percentile‚Äîthose exactly at the median‚Äîare assigned a score of 100. But since I.Q.s are always rising, the only way to keep that hundred-point benchmark is periodically to make the tests more difficult‚Äîto ‚Äúrenorm‚Äù them. The original WISC was normed in the late nineteen-forties. It was then renormed in the early nineteen-seventies, as the WISC-R; renormed a third time in the late eighties, as the WISC III; and renormed again a few years ago, as the WISC IV‚Äîwith each version just a little harder than its predecessor. The notion that anyone ‚Äúhas‚Äù an I.Q. of a certain number, then, is meaningless unless you know which WISC he took, and when he took it, since there‚Äôs a substantial difference between getting a 130 on the WISC IV and getting a 130 on the much easier WISC.
Link to Malcolm Gladwell article in the New Yorker.