Since the discussion on Chris’ post on mumbo-jumbo went straight from the ludicrous Edward de Bono to the Flynn effect, I thought I’d repost a lightly edited version of a piece on the Flynn effect and The Bell Curve that was on my own blog a couple of months ago, but might be of interest to CT readers.
The Bell Curve got a thorough hammering on statistical grounds when it came out (this review by conservative economist Jim Heckman in Reason is damning, and it was one of the polite ones). But the thing that most annoyed me when I read it was their discussion of the Flynn effect, namely that average scores on IQ tests have risen steadily over time, by amounts sufficient to wipe out the differences between racial groups on which Murray and Herrnstein rely. As Thomas Sowell points out in this review (reproduced by Brad de Long), it’s hard to see how any claim that differences in IQ test scores observed in Western societies are mostly due to genetic factors can stand up in the face of this observation. But Murray and Herrnstein slide straight past it, saying that they are concerned with contemporary inequality, not with time trends. This is about as reasonable as a “nurturist” deciding to ignore twin studies on the grounds that most people aren’t twins.
I think there are two reasonable interpretations of the Flynn effect. One is to agree with Murray and Herrnstein that IQ test scores measure “intelligence” and to conclude that intelligence is primarily determined by environmental factors, and particularly by education.
The second is that IQ tests scores do not, in fact, correspond to what we normally mean by intelligence but to something narrower, and more environmentally malleable. The simplest version of this would be to suppose that IQ tests measure the capacity to solve IQ test problems and to attribute the Flynn effect to “test sophistication”, the fact that people who have done IQ tests in the past do better. The problem is that the administration of IQ tests to kids was probably more common 50 years ago than today.
A more plausible claim is that IQ tests are essentially academic achievement/aptitude tests. They are ‘content-free’ in that they don’t rely on information from specific courses in the manner of school assessments, but they do test skills that are promoted by school education and by an environment where most people have high (by historical standards) levels of education. They are good predictors of university performance (thanks for this link to Jack Strocchi). Since academic aptitude naturally rises with education we would expect to get the obvious virtuous circle – the more schooling there is, the higher is IQ and the more kids are capable of benefitting from a university education.
While it’s implausible that the population is massively more intelligent than it was a couple of generations ago, it’s not unreasonable to suggest that capacity for academic achievement has been rising steadily. Fifty years ago, someone who suggested that the majority of people were capable of getting a university degree would have been regarded as utopian. And despite the dumbing down of the last decade or so, the content of the average degree is probably tougher now than fifty years ago.
On the other hand, I imagine that, if there were tests that depended, even subtly, on familiarity with agriculture, scores would have plummeted over the same period.
I’m happy with the idea that intelligence is more than IQ. But of course, the evidence on which Murray and Herrnstein rely is all about IQ scores. This evidence shows, about as unambiguously as is possible, that changes in the environment can substantially increase the average IQ score of a population with a broadly constant genetic endowment.