The Bell Curve Flattened

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Jan. 18 1997 3:30 AM

The Bell Curve Flattened

Subsequent research has seriously undercut the claims of the controversial best seller.

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Charles Murray is a publicity genius, and the publication of his and Richard Herrnstein's book, The Bell Curve: Intelligence and Class Structure in American Life, in the fall of 1994 was his masterpiece.

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Virtually all ambitious trade hardcover books are preceded by an edition of 100 to 200 flimsy "galley proofs." These are sent out to people who might generate buzz for the book: blurbists, bookers for television talk shows, editors, and--most important--book critics. There is an ethos of letting the chips fall where they may about the sending out of galleys: Now the book will begin to receive uncontrolled reaction. (For example, back in 1991, Murray somehow got hold of the galleys of my own last book, and wrote me heatedly denying that he was working on a book about black genetic intellectual inferiority, as I had asserted. I left the passage in, but softened it.)

The Bell Curve was not circulated in galleys before publication. The effect was, first, to increase the allure of the book (There must be something really hot in there!), and second, to ensure that no one inclined to be skeptical would be able to weigh in at the moment of publication. The people who had galley proofs were handpicked by Murray and his publisher. The ordinary routine of neutral reviewers having a month or two to go over the book with care did not occur. Another handpicked group was flown to Washington at the expense of the American Enterprise Institute and given a weekend-long personal briefing on the book's contents by Murray himself (Herrnstein had died very recently), just before publication. The result was what you'd expect: The first wave of publicity was either credulous or angry, but short on evidence, because nobody had had time to digest and evaluate the book carefully.

The Bell Curve isn't a typical work of trade nonfiction. It is gotten up as a work of original scholarly research. Most works containing fresh regression analysis and historical argument from primary sources would be published in academic quarterlies that send manuscripts out for elaborate, lengthy evaluation before deciding whether to publish them. Herrnstein and Murray didn't do this, so it wasn't until a full year or more after The Bell Curve was published that the leading experts on its subject had a chance to go through the underlying data with care. Therefore, as time went on, the knowledgeability of the Bell Curve discussion grew, but the attention paid to that discussion inevitably shrank.

The debate on publication day was conducted in the mass media by people with no independent ability to assess the book. Over the next few months, intellectuals took some pretty good shots at it in smaller publications like the New Republic and the New York Review of Books. It wasn't until late 1995 that the most damaging criticism of The Bell Curve began to appear, in tiny academic journals. What follows is a brief summary of that last body of work. The Bell Curve, it turns out, is full of mistakes ranging from sloppy reasoning to mis-citations of sources to outright mathematical errors. Unsurprisingly, all the mistakes are in the direction of supporting the authors' thesis.

First, a quick précis of The Bell Curve. IQ tests, according to Murray and Herrnstein, measure an essential human quality, general intelligence. During the second half of the 20th century, this quality has risen to supreme importance, because society has become increasingly complex. The intelligent have therefore gone through an "invisible migration," from points of origin all over the class system to a concentration at the top of business, government, and the professions. They are likely to become ever more dominant and prosperous. The unintelligent are falling further and further behind. Because intelligence is substantially inherited, nothing is likely to reverse this process. Blacks are overrepresented among the unintelligent. Any efforts government might make to improve the economic opportunities of poor people, especially poor black people, are likely to fail, because their poverty is so much the result of inherited low intelligence. About the best that can be done for these people is an effort to create a world of simple, decent, honorable toil for them.

Herrnstein and Murray begin by telling us that the liberal position on IQ--namely, "Intelligence is a bankrupt concept"--has been discredited, and that "a scholarly consensus has been reached" around their position. This consensus is "beyond significant technical dispute." Thus, by the end of their introduction, they have arranged matters so that if intelligence has any meaning at all, the idiotic liberals stand discredited; and meanwhile, extremely broad claims for intelligence have the cover of "consensus."

The notion that IQ tests are completely useless never prevailed in liberal academia to nearly the extent that Herrnstein and Murray say. A more accurate rendering of the liberal position would be that rather than a single "general intelligence," there are a handful of crucial--and separate--mental abilities; that none of these abilities is important enough to obviate the role of family background and education; and that native ability (and economic success independent of native ability) can be enhanced by improving education, training, and public health. The Bell Curve refers in passing to some of these points, but on the whole it sets up a cartoon-left position as its (easy) target. Meanwhile, the psychometricians who dominate the footnotes of The Bell Curve are John Hunter, Arthur Jensen, Malcolm Ree, and Frank Schmidt. These men are well known within the field as representing its right wing, not a mainstream consensus.

The next problem with The Bell Curve's thesis is in the idea of the rise to dominance of the cognitive elite. To the book's initial audience of Ivy Leaguers, this idea seemed valid on its face. Everybody knows that the best universities, law firms, hospitals, investment banks, and the State Department used to be run by preppies whose main virtue was fortunate birth, and are now open to one and all on the basis of merit.

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B ut the larger premise--that intelligent people used to be scattered throughout the class structure, and are now concentrated at the top--is almost impossible to prove, simply because the mass administration of mental tests is such a recent phenomenon. High scorers on mental tests do "bunch up" (as Herrnstein and Murray put it) in elite-university student bodies. But this is tautological: Any group selected on the basis of scores on mental tests will be composed disproportionately of people who score high on mental tests. Proving The Bell Curve's thesis would require proving that success increasingly correlates with IQ in areas of life where mental tests are not the explicit gatekeepers. To see how The Bell Curve tries and fails to get around these inherent problems, see and.

Having conditioned its audience to view IQ as all-important, The Bell Curve then manipulates statistics in a way that makes IQ look bigger, and everything else smaller, in determining Americans' life-chances.

The basic tool of statistical social science in general, and of The Bell Curve in particular, is regression analysis, a technique used to assign weights to various factors (called "independent variables") in determining a final outcome (called the "dependent variable"). The original statistical work in The Bell Curve consists of regression analyses on a database called the National Longitudinal Study of Youth. The authors claim to demonstrate that high IQ is more predictive of economic success than any other factor, and that low IQ is more predictive of poverty and social breakdown. Virtually all the early commentators on The Bell Curve were unable to assess the merits of the regression analysis. "I am not a scientist. I know nothing about psychometrics," wrote Leon Wieseltier (who was otherwise quite critical) in a typical disclaimer.

But by now the statistics have been gone over by professionals, who have come up with different results. The key points of their critique of The Bell Curve are as follows:

What Herrnstein and Murray used to measure IQ is actually a measure of education as well as intelligence. All the people tracked in the National Longitudinal Study of Youth took the Armed Forces Qualifying Test, which Herrnstein and Murray treat as a good measure of intelligence. Because the material covered in the test includes subjects like trigonometry, many academic critics of The Bell Curve have objected to its use as a measure only of IQ and not at all of academic achievement. Herrnstein and Murray concede in the footnotes that scores tend to rise with the subjects' education--but they seriously underestimate the magnitude of this rise, as shows. And they resist the obvious inference that the test scores are measuring something other than intelligence.

Most of The Bell Curve's analysis is devoted to proving that IQ has more predictive power than parental "socio-economic status." But Herrnstein and Murray's method of figuring socioeconomic status seems designed to low-ball its influence, as explains.

Herrnstein and Murray begin their discussion of the National Longitudinal Study of Youth data by announcing that they aren't going to analyze the effect of education, because education is too much a result of IQ. It's not an independent variable. (Of course, according to their theory, socioeconomic status is also a result of IQ, but somehow, that doesn't stop them.) Therefore, what you'd most want to know from a policy standpoint--how much education can increase opportunity--isn't dealt with in the book, except in two obscure footnotes. Both would seem to support the liberal, pro-education position that Herrnstein and Murray say is futile. One footnote shows education increasing IQ year by year. The other shows a higher correlation between college degree and family income than between IQ and family income.

One of The Bell Curve's theoretical linchpins is the high heritability of IQ. Herrnstein and Murray, sounding like the souls of caution, write that "half a century of work, now amounting to hundreds of empirical and theoretical studies, permits a broad conclusion that the genetic component of IQ is unlikely to be smaller than 40 per cent or higher than 80 per cent. ... For purposes of this discussion, we will adopt a middling estimate of 60 per cent heritability." This now looks seriously overstated. Michael Daniels, Bernie Devlin, and Kathryn Roeder of Carnegie Mellon University took the same studies on which Herrnstein and Murray based their estimate, and subjected them to a computer meta-analysis ("a powerful method of statistical analysis"--The Bell Curve). Their paper, which has not yet been published, says: "In brief, studies of IQ, and our reanalyses of them, suggest a narrow-sense heritability of 34 per cent and a broad-sense heritability of 46 per cent. [The difference between broad and narrow is too technical to explain in this limited space.] This is a far cry from Herrnstein and Murray's maximum value of 80 per cent or their middling value of 60 per cent. Consequently, Herrnstein and Murray give the impression that IQ is highly 'heritable,' but it is not."

If the purpose of the whole exercise is to figure out what our social policies should be, then, "Which is more predictive, IQ or socioeconomic status?" isn't the essential question anyway. Making it the essential question avoids the issue of whether IQ is really so massively predictive that it drowns out everything else. (Herrnstein and Murray mostly leave the evidence for this, their central contention, to footnotes. The figures they offer are far from dispositive.)

The chapter of The Bell Curve on policies that might be able to overcome the fate of a low IQ focuses mainly on whether early-childhood programs like Head Start (most of which aren't run with raising IQ as their primary goal) can raise IQ significantly over the long term, and sorrowfully concludes that they can't. What the book doesn't discuss is whether public schools--by far the biggest government social program--can raise IQ, or earnings after you control for IQ. As James Heckman of the University of Chicago wrote in the Journal of Political Economy, " Evidence of a genetic component to skills has no bearing on the efficacy of any social policy. ... The relevant issue is the cost effectiveness of the intervention." (As an example of where the kind of analysis Herrnstein and Murray didn't do can lead, a new study by Jay Girotto and Paul Peterson of Harvard shows that students who raise their grades and take harder courses can increase their IQ scores by an average of eight points during the first three years of high school.)

At the beginning of The Bell Curve, Herrnstein and Murray declare that "the concept of intelligence has taken on a much higher place in the pantheon of human virtues than it deserves." And they claim that their view of IQ tests is "squarely in the middle of the scientific road." They end by expressing the hope that we can "be a society that makes good on the fundamental promise of the American tradition: the opportunity for everyone, not just the lucky ones, to live a satisfying life." Throughout, Herrnstein and Murray consistently present themselves as fair- (or even liberal-) minded technicians who have, with great caution, followed the evidence where it leads--which, unfortunately, is to a few unassailable if unpleasant scientific truths that it is their reluctant duty to report.

In fact, The Bell Curve is a relentless brief for the conservative position in psychometrics and social policy. For all its talk of reflecting a consensus, the sources it draws upon are heavily skewed to the right. Herrnstein and Murray used quasi-nutty studies that support their position (as Charles Lane demonstrated in the New York Review of Books), and ignore mainstream studies that contradict it (as Richard Nisbett showed in the New Republic). The data in The Bell Curve are consistently massaged to produce conservative conclusions; not once is a finding that contradicts the main thesis reported in the text. (shows how Herrnstein and Murray have made the convergence in black-white IQ scores, which they claim to find "encouraging," look smaller than it actually is.) The Bell Curve's air of strict scientism doesn't preclude the use of lightly sourced or unsourced assertions, such as the statement that the median IQ of all black Africans is 75, or that "intermarriage among people in the top few percentiles of intelligence may be increasing far more rapidly than suspected" (no footnote). Though they piously claim not to be doing so, Herrnstein and Murray leave readers with the distinct impression that IQ is the cause of economic success and failure, and that genetic difference explains the black-white IQ gap.

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In the most famous passage in The Republic, Plato describes an underground cave where people are held prisoner in chains, unable to see anything but the shadows cast by figures passing outside; they mistake the shadows for reality. The Republic is probably the first place in history where an idea like that of Murray and Herrnstein's cognitive elite appears. Plato believed that through education, people could leave the cave and be able to see the truth instead of the shadows, thus fitting themselves to become the wise rulers of society. But he was quick to insert a cautionary note: Those who have left the cave might be tempted to think they can see perfectly clearly, while actually they would be "dazzled by excess of light." The image applies to The Bell Curve: Presented as an exact representation of reality, in opposition to the shadows of political correctness, it actually reflects the blinkered vision of one part of the American elite. It constantly tells these people that they are naturally superior, and offers lurid descriptions of aspects of national life that they know about only by rumor. Readers who accept The Bell Curve as tough-minded and realistic, and who assume that all criticism of it is ignorant and ideologically motivated, are not as far removed from Plato's cave as they might think.

: Dumb College Students

: Smart Rich People

: Education and IQ

: Socioeconomic Status

: Black-White Convergence

Nicholas Lemann is national correspondent of the Atlantic.

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