Bell Curve


 * See normal distribution for the "bell curve" in statistics.

The Bell Curve is a controversial, best-selling 1994 book by Richard J. Herrnstein and Charles Murray exploring the role of intelligence in American life. The authors became notorious for the book's discussion of race and intelligence in Chapters 13 and 14.

Named for the bell-shaped normal distribution of IQ scores, the book cites the rise of a "cognitive elite" having a significantly higher than average chance of succeeding in life.

Within both the mainstream media and the scientific community, large numbers of people rallied to both support and criticize the book. Some critics denounced the book and its authors as supporting scientific racism.

Summary of contents
The Bell Curve is fairly large for a book of its popularity, weighing in at 845 pages in the first printing and 879 in the revised paperback form. Much of its material is technical and academic, but the book's statistical explanations are styled to appeal to a general audience. There are extensive notes, graphs, and tables.

The Bell Curve is divided into four sections.
 * Part I argues that social stratification on the basis of intelligence has been increasing since the beginning of the twentieth century.
 * Part II presents original research showing significant correlations between intelligence and various social and economic outcomes.
 * Part III, by far the most controversial, examines what role IQ plays in contributing to social and economic differences between ethnic groups in America.
 * In Part IV, the authors discuss the implications of their findings for education and social policy in the United States.

Herrnstein and Murray in many ways follow in the footsteps of Harvard researcher Arthur Jensen.

They argue in the book that 1) intelligence exists and is accurately measureable across racial, language, and national boundaries, 2) intelligence is one of -- if not the most -- important correlative factor in economic, social, and success in general in America, and is becoming more important, 3) intelligence is largely to mostly (40% to 80%) genetically heritable, 4) there are racial and ethnic differences in IQ that cannot be sufficiently explained by environmental factors such as nutrition, social policy, or racism, 5) nobody has so far been able to manipulate IQ long term to any significant degree through changes in environmental factors, and in light of their failure such approaches are becoming less promising, and finally, 6) as a country the USA has been in denial of these facts, and in light of these findings a better public understanding of the nature of intelligence and its social correlates is necessary to guide future policy decisions in America.

Their evidence comes from an analysis of data compiled in the National Longitudinal Study of Youth (NLSY), a study conducted by the U.S. Department of Labor's Bureau of Labor Statistics tracking thousands of Americans starting in the 1980s. All participants in the NLSY took the Armed Forces Qualifying Test (AFQT), a measure of cognitive ability comparable to an IQ test. Participants were later evaluated for social and economic outcomes. In general, IQ/AFQT scores were a better predictor of life outcomes than social class background. Similarly, after statistically controlling for differences in IQ, many outcome differences between racial-ethnic groups disappeared. (see also Significance of group IQ differences)

Responses
Upon publication, The Bell Curve received a great deal of positive publicity, including cover stories in Newsweek ("the science behind [it] is overwhelmingly mainstream"), early publication (under protest by other writers and editors) by The New Republic by its editor-in-chief at the time Andrew Sullivan, and The New York Times Book Review (which suggested critics disliked its "appeal to sweet reason" and are "inclined to hang the defendants without a trial"). Early articles and editorials appeared in Time, The New York Times ("makes a strong case"), The New York Times Magazine, Forbes, the Wall Street Journal, and The National Review. It received a respectful airing on such shows as Nightline, the MacNeil/Lehrer NewsHour, the McLaughlin Group, Think Tank, PrimeTime Live, and All Things Considered. The book sold over 300,000 copies in hardcover.

While the book's popularity was mostly propelled by its controversial claims regarding race and intelligence, both the accuracy of those claims and the qualifications of the authors soon came under attack. Dr. Herrnstein died before the book was released, leaving Charles Murray to do most of its public defense. Although Herrnstein was a prominent psychologist, Murray has a Ph.D. in political science with no formal credentials in psychometrics.

Some scientific response to The Bell Curve has been highly negative. Georgetown University Distinguished Professor of Health Studies Craig T. Ramey said "Within the sophisticated research community, the opinion has been virtually unanimous that The Bell Curve was a primitive, oversimplistic and flawed analysis." University of Oklahoma Assistant Professor of Anthropology Michael Nunley wrote:


 * I believe this book is a fraud, that its authors must have known it was a fraud when they were writing it, and that Charles Murray must still know it's a fraud as he goes around defending it. [...] After careful reading, I cannot believe its authors were not acutely aware of [...] how they were distorting the material they did include.

Professor Leon Kamin, a longtime critic of cognitive ability tests, said the book did "a disservice to and abuse of science." Boston University Neurology Professor Howard Gardner (who, like Kamin and some of the other critics, holds views which are criticized by Herrnstein and Murray) called the style of thought "scholarly brinkmanship":


 * The authors seem to show the evidence and leave the implications for the reader to figure out; discussing scientific work on intelligence, they never quite say that intelligence is all important and tied to one's genes, yet they signal that this is their belief and that readers ought to embrace the same conclusions.

Economist and conservative writer Thomas Sowell, who is black (a racial group identified in the book as having a lower average IQ than some other racial groups), criticized some aspects of the book, claiming that the authors ignored data and failed to draw obvious conclusions from it that would have hurt their argument. But he nonetheless concluded that "The Bell Curve is a very sober, very thorough, and very honest book." 

In its defense, fifty-two professors, including researchers in the study of intelligence and related fields, signed a statement titled "Mainstream Science on Intelligence" supporting many of the scientific views reported in The Bell Curve. The statement was written by psychometrics researcher Linda Gottfredson and published in The Wall Street Journal in 1994 and later in the journal Intelligence. Some of the signers had previously made similar claims about race and intelligence and were cited as sources in the book.

Race and intelligence research is often considered a taboo subject. Charles Murray noted, for example, "Some of the things we read to do this work, we literally hide when we're on planes and trains". Critics have noted much of the work referenced by the Bell Curve was funded by the Pioneer Fund, which aims to advance the scientific study of heredity and human differences, and has been accused of promoting scientific racism. Critics argue the book was written to encourage politically-beneficial racism, citing Murray's book proposal which described the target audience as the "huge number of well-meaning whites who fear that they are closet racists, and this book tells them they are not. It's going to make them feel better about things they already think but do not know how to say." (New York Times Magazine, 10/9/94)

American Psychological Association task force report
In response to the growing controversy surrounding The Bell Curve, the American Psychological Association's Board of Scientific Affairs established a special task force to publish an investigative report on the research presented in the book. The full text of the report is available at a third-party website. 

Many of the task force's findings supported statements from The Bell Curve. They agreed that IQ scores have high predictive validity for individual differences in school achievement. They also confirm the predictive validity of IQ for adult occupational status, even when variables such as education and family background have been statistically controlled. They agree that individual differences in intelligence are substantially influenced by genetics. Consistent with Herrnstein and Murray's findings, they state there is little evidence to show that childhood diet influences intelligence except in cases of severe malnutrition. They agree that there are no significant differences between the IQ scores of males and females. Perhaps most significantly, the APA task force agrees that there do exist large differences between the average IQ scores of blacks and whites, and that these differences cannot be attributed to biases in test construction, nor do they merely reflect differences in socio-economic status between the ethnic groups.

The APA task force concluded that "many of the critical questions about intelligence are still unanswered", although it is believed that both genetic and environmental contribute substantially to individual differences in (psychometric) intelligence. Regarding the alleged genetic influence of genetic factors on IQ differentials between the mean intelligence test scores of Blacks and Whites, the APA report concludes (no. 6):"there is certainly no such support for a genetic interpretation. At present, no one knows what causes this differential".

Stephen Jay Gould's criticisms
Perhaps the most prominent critic of The Bell Curve was the late Stephen Jay Gould, who in 1996 released a revised and expanded edition of his 1981 work The Mismeasure of Man intended to refute many of The Bell Curve's claims regarding race and intelligence. Specifically, Gould argues that the current evidence showing heritability of IQ does not indicate a genetic origin to group differences in intelligence. Murray claims that Gould misstated his claims; for instance, Gould says Murray boils down intelligence to a single factor while Murray denies making such a claim.

Arthur Jensen, Professor of Educational Psychology, University of California, Berkeley, responds to Gould's criticisms in a paper titled The Debunking of Scientific Fossils and Straw Persons.

Other criticisms
A minority of critics have objected not only to Herrnstein and Murray's conclusions, but to their statistical methodology as well. The Sociology Department of the University of California, Berkeley published a critical analysis of The Bell Curve under the title Inequality by Design. The book reviews The Bell Curve's statistical analyses and claims that it contains technical errors and omissions. Another statistical critique of the book was published by James Heckman in 1995. Murray responded to a shorter version of Heckman's critique in an August 1995 letter exchange in Commentary magazine.

In Intelligence, Genes, and Success: Scientists Respond to The Bell Curve a group of social scientists and statisticians analyzes the genetics-intelligence link, the concept of intelligence, the malleability of intelligence and the effects of education, the relationship between cognitive ability, wages and meritocracy, pathways to racial and ethnic inequalities in health, and the question of public policy.

Another popular book written at least in part to refute some of The Bell Curve's claims is the Pulitzer Prize-winning Guns, Germs, and Steel: The Fates of Human Societies, by Jared Diamond. Diamond argues that the differences in technology produced by various races are the result of differences in factors like terrain or the availability of natural resources, not of differences in intelligence.

A recent paper in the Psychological Review, "Heritability Estimates Versus Large Environmental Effects: The IQ Paradox Resolved" presents a mechanism by which environmental effects on IQ may be magnified by feedback effects. This approach may provide a resolution of the contradiction between the viewpoint of The Bell Curve and its supporters, and the 'nurture' factors of IQ believed to exist by its critics.

Arthur Jensen (1994) wrote in National Review:
 * Consideration of the book's actual content is being displaced by the rhetoric of denial: name calling ("neo-nazi," "pseudo-scientific," "racism"), sidetracks ("but does IQ really measure intelligence?"), non-sequiturs ("specific genes for IQ have not been identified, so we can claim nothing about its heritability"), red herrings ("Hitler misused genetics"), falsehoods ("all the tests are biased"), hyperbole ("throwing gasoline on a fire"), and insults ("creepy," "indecent," "ugly").

Miscellanea
From 1986 to 1989, Murray was given an annual grant by the conservative Bradley Foundation of $90,000, rising to $113,000 by 1991, and then to $163,000 following publication of The Bell Curve.

According to an American Broadcasting Company news report, the Pioneer Fund contributed $3.5 million to researchers cited in The Bell Curve, and almost half of the research cited to support the most controversial racial conclusions of the book was paid for by the Pioneer Fund. 

The Bell Curve provided the first discussion of the Flynn effect aimed at a general audience, and was the first work to refer to it by that name (pp. 307–09).

Arguments against The Bell Curve

 * Fairness and Accuracy in Reporting, Racism Resurgent: How Media Let The Bell Curve's Pseudo-Science Define the Agenda on Race
 * Critical analysis of Bell Curve methodology
 * The Return of Determinism? The Pseudoscience of the Bell Curve
 * "The Bell Curve Flattened: Subsequent research has seriously undercut the claims of the controversial best seller."
 * Nobel Prize-winner James Heckman, "Lessons from the Bell Curve", Journal of Political Economy, October 1995.

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