The Bell Curve

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

The Bell Curve

Author	Richard Herrnstein, Charles Murray
Publisher	Free Press
Publication date	September 1994
Media type	Hardcover
ISBN	ISBN 0-02-914673-9

The Bell Curve is a controversial, best-selling 1994 book by Richard J. Herrnstein and Charles Murray exploring the relationship between intelligence and society in American life. Named for the bell-shaped normal distribution of IQ scores, the book claims that Americans of high intelligence form a "cognitive elite" who have a significantly higher-than-average chance of succeeding in life, as do their children. The book became widely read and debated due to its discussion of race and intelligence in Chapters 13 and 14, where the authors make the controversial claim that blacks, on average, are less intelligent than whites and Asians, and that this difference might be due in part to genetic factors.

Shortly after publication, large numbers of people rallied both to criticize and defend the book. Some critics denounced the book and its authors as supporting scientific racism.

Content

The Bell Curve is fairly large for a book of its popularity, having 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. Template:ImageStackRight 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. For instance, based on data as of 1989 this section shows that among Whites, intelligence level (cognitive class) is a better predictor of poverty than parents' socioeconomic class as shown on the summary table below:

Percentage in Poverty

Category	Parents' socioeconomic class	Cognitive class
Very high\Very bright	3	2
High\Bright	3	3
Average	7	6
Low\Dull	12	16
Very low\Very dull	24	30
Overall average	7	7

Part III, by far the most controversial, examines what role IQ plays in contributing to social and economic differences between ethnic groups in America.

Part IV discusses the implications of the findings for education and social policy in the United States.

Herrnstein and Murray in many ways follow in the footsteps of UC Berkeley researcher Arthur Jensen, whose controversial article on the subject appeared in 1969 in the Harvard Educational Review. The Bell Curve argues that:

1. Intelligence exists and is accurately measurable across racial, language, and national boundaries.
2. Intelligence is one, if not the most, important correlative factor in economic, social, and overall success in America, and is becoming more important.
3. Intelligence is largely (40% to 80%) genetically heritable.
4. There are racial and ethnic differences in IQ that cannot be entirely explained by environmental factors such as nutrition, social policy, or racism.
5. No one has so far been able to manipulate IQ long term to any significant degree through changes in environmental factors - except for child adoption - and in light of their failure such approaches are becoming less promising.
6. The USA has been in denial regarding 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.)

Economic and social correlates of IQ

IQ	<75	75-90	90-110	110-125	>125
US population distribution	5	20	50	20	5
Married by age 30	72	81	81	72	67
Out of labor force more than 1 month out of year (men)	22	19	15	14	10
Unemployed more than 1 month out of year (men)	12	10	7	7	2
Divorced in 5 years	21	22	23	15	9
% of children w/ IQ in bottom decile (mothers)	39	17	6	7	-
Had an illegitimate baby (mothers)	32	17	8	4	2
Lives in poverty	30	16	6	3	2
Ever incarcerated (men)	7	7	3	1	0
Chronic welfare recipient (mothers)	31	17	8	2	0
High school dropout	55	35	6	0.4	0
Values are the percentage of each IQ sub-population, among non-Hispanic whites only, fitting each descriptor. Herrnstein & Murray (1994) pp. 171, 158, 163, 174, 230, 180, 132, 194, 247-248, 194, 146 respectively.

Policy recommendations

Herrnstein and Murray recommended the elimination of welfare programs (p. 548):

We can imagine no recommendation for using the government to manipulate fertility that does not have dangers. But this highlights the problem: The United States already has policies that inadvertently social-engineer who has babies, and it is encouraging the wrong women. If the United States did as much to encourage high-IQ women to have babies as it now does to encourage low-IQ women, it would rightly be described as engaging in aggressive manipulation of fertility. The technically precise description of America's fertility policy is that it subsidizes births among poor women, who are also disproportionately at the low end of the intelligence distribution. We urge generally that these policies, represented by the extensive network of cash and services for low-income women who have babies, be ended.

This claim spurred later research in economics and sexology, which considered that welfare programs for females had a doubly negative effect on aggregate IQ within the transfer group, by allowing the female partner to forgo a full consideration of the male's ability to serve as a provider of familial resources, instead placing greater emphasis on desirable physical or social characteristics (presumed to be not as positively correlated with IQ). Neither of these claims, as originally embodied in text and the follow-on research, dealt with race as such, but rather demonstrated concern that large numbers of minorities were positioned as recipients, leading to a continual worsening of the measured divergence in intelligence. However, two years later, the 1996 U.S. welfare reform substantially cut these programs.

In a discussion of the future political outcomes of an intellectually stratified society, they stated that they "fear that a new kind of conservatism is becoming the dominant ideology of the affluent - not in the social tradition of an Edmund Burke or in the economic tradition of an Adam Smith but 'conservatism' along Latin American lines, where to be conservative has often meant doing whatever is necessary to preserve the mansions on the hills from the menace of the slums below" (p. 518). Moreover, they fear that an increasing welfare will create a "custodial state" in which "a high-tech and more lavish version of the Indian reservation for some substantial minority of the nation's population." They also predict increasing totalitarianism: "It is difficult to imagine the United States preserving its heritage of individualism, equal rights before the law, free people running their own lives, once it is accepted that a significant part of the population must be made permanent wards of the states" (p. 526).

Responses

Initially, 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 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. [9] The book sold over 500,000 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 in the media. 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 scholars have condemned the book. 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." Harvard University Education 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.

African-American economist and conservative writer Thomas Sowell criticized the books conclusions about race and the malleablility of IQ writing:

When European immigrant groups in the United States scored below the national average on mental tests, they scored lowest on the abstract parts of those tests. So did white mountaineer children in the United States tested back in the early 1930s... Strangely, Herrnstein and Murray refer to "folklore" that "Jews and other immigrant groups were thought to be below average in intelligence." It was neither folklore nor anything as subjective as thoughts. It was based on hard data, as hard as any data in The Bell Curve. These groups repeatedly tested below average on the mental tests of the World War I era, both in the army and in civilian life. For Jews, it is clear that later tests showed radically different results--during an era when there was very little intermarriage to change the genetic makeup of American Jews.

In its defense, fifty-two professors, including researchers in the study of intelligence and related fields, signed a statement titled "Mainstream Science on Intelligence"[10] supporting virtually all 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[11]. Some of the signers had previously made similar claims about race and intelligence and had been cited as sources in the book.

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 final report, titled Intelligence: Knowns and Unknowns, is available at a third-party website. [12]

Some of the task force's findings supported or were consistent with statements from The Bell Curve. They agreed that:

• IQ scores have high predictive validity for individual differences in school achievement.
• IQ scores have predictive validity for adult occupational status, even when variables such as education and family background have been statistically controlled.
• Individual differences in intelligence are substantially influenced by genetics.
• Individual differences in intelligence are substantially influenced by environment as well.
• There is little evidence to show that childhood diet influences intelligence except in cases of severe malnutrition.
• There are no significant differences between the IQ scores of males and females.

Regarding statements regarding racial differences and genetics, the APA task force stated:

There is certainly no such support for a genetic interpretation....It is sometimes suggested that the Black/ White differential in psychometric intelligence is partly due to genetic differences (Jensen, 1972). There is not much direct evidence on this point, but what little there is fails to support the genetic hypothesis.

Regarding statements about other explanations for racial differences, the APA task force stated:

The differential between the mean intelligence test scores of Blacks and Whites (about one standard deviation, although it may be diminishing) does not result from any obvious biases in test construction and administration, nor does it simply reflect differences in socio-economic status. Explanations based on factors of caste and culture may be appropriate, but so far have little direct empirical support.

Regarding statements about any explanations for racial differences, the APA task force stated:

At present, no one knows what causes this differential.

The APA journal that published the statement, American Psychologist, subsequently published eleven critical responses in January 1997, most arguing that the report failed to examine adequately the evidence for and against partly-genetic explanations of Black-White differences in mean IQ . Charles Murray, for instance, responded:

Actually, there is no direct evidence at all, just a wide variety of indirect evidence, almost all of which the task force chose to ignore.

See also: the discussion of intelligence testing

Criticisms

It is doubtful whether any book in the entire history of psychology has been so extensively attacked as The Bell Curve. 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 controversial book 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.

The initial positive reception of The Bell Curve in media such as newspapers and television talk shows was troubling to critics such as economist Edward S. Herman and evolutionary biologist Joseph L. Graves who felt that it indicated a troubling acceptance of what Herman calls deterministic racist doctrines. Dennis M. Rutledge suggests that through soundbites of works like Jensen's famous study on the achievement gap, and Herrnstein and Murray's book The Bell Curve, the media "paints a picture of Blacks and other people of color as collective biological illiterates-- as not only intellectually unfit but evil and criminal as well." thus providing, he says "the logic and justification for those who would further disenfranchise and exclude racial and ethnic minorities."

Flawed assumptions

Much of the criticism of The Bell Curve has focused on the potential for faults in the basic assumptions made at the beginning of the book. William J. Matthews and Stephen Jay Gould list four basic assumptions of The Bell Curve:

1. Intelligence must be depictable as a single number.
2. Intelligence must be capable of rank ordering people in a linear order.
3. Intelligence must be primarily genetically based.
4. Intelligence must be essentially immutable.

If any of these premises are false then their entire argument disintegrates (Gould, 1994). Similarly, in "Science" in the service of Racism C. Loring Brace writes that The Bell Curve makes six basic assumptions at the beginning of the book:

1. Human Cognitive ability is a single general entity, depictable as a single number.
2. Cognitive ability has a heritability of between 40 and 80 percent and is therefore primarily genetically based.
3. IQ is essentially immutable, fixed over the course of a life span.
4. IQ tests measure how "smart" or "intelligent" people are and are capable of rank ordering people in a linear order.
5. IQ test can measure this accurately.
6. IQ tests are not biased with regard to race ethnic group or socioeconomic status.

Brace proceeds to argue that there are faults in every one of these assumptions. Nobel prize winning statistician James Heckman writes that two assumptions made in the book are questionable:

1. "g" accounts for correlation across test scores and performance in society.
2. "g" cannot be manipulated.

Heckman writes that a reanalysis of the evidence used in The Bell Curve contradicts this story. The factors that explain wages receive different weights than the factors that explain test scores. More than "g" is required to explain either. Other factors besides "g" contribute to social performance, and they can be manipulated. Murray responded to a shorter version of Heckman's critique in an August 1995 letter exchange in Commentary magazine.

Flawed methodology

Michael Hout of the University of California at Berkeley, along with five colleagues, recalculated the effect of socioeconomic status, using the same variables as The Bell Curve but weighting them differently. They found that if IQ scores are corrected to eliminate the effect of education as Herrnstein and Murrays did, the the ability of IQ to predict poverty can be made to look dramatically overstated by as much as 61 percent for whites and 74 percent for blacks. In other words, according to Hout et al., Herrnstein and Murray's key finding, that IQ predicts poverty much better than socioeconomic status does, is substantially a result of the way they handled the statistics. In a paper titled A Reanalysis of The Bell Curve researchers found that Herrnstein and Murray`s measure of parental socioeconomic status failed to capture the effects of important elements of family background (such as single-parent family structure at age 14). As a result, their analysis gave an exaggerated impression of the importance of IQ relative to parents` SES, and relative to family background.

In the book 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. This work argues that much of the public response was polemic and failed to analyze the details of the science and validity of the statistical arguments underlying the book's conclusions.

Contradictory findings

Min-Hsiung Huang and Robert M. Hauser found that, controlling for social background, the Black-White test score gap narrowed significantly over the period from 1974 to 1998. These results provide no support for any of the trend hypotheses advanced by Herrnstein and Murray

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. Janet Currie and Duncan Thomas presented evidence suggesting AFQT scores are likely better markers for family background than "intelligence" in a 1999 Study.

Herrnstein and Murray report that conditional on maternal "intelligence" (AFQT scores), child test scores are little affected by variations in socio-economic status. Using the same data, we demonstrate their finding is very fragile.

Charles R. Tittle, Thomas Rotolo found that the more written, IQ-like examinations are used as screening devices for occupational access, the stronger the relationship between IQ and income. Thus, rather than higher IQ leading to status attainment because it indicates skills needed in a modern society, IQ may reflect the same test-taking abilities used in artificial screening devices by which status groups protect their domains. Min-Hsiung Huang and Robert M. Hauser write that Herrnstein and Murray provide scant evidence of growth in cognitive sorting. Using data from the General Social Survey, they tested each of these hypotheses using a short verbal ability test which was administered to about 12,500 American adults between 1974 and 1994 the results provided no support for any of the trend hypotheses advanced by Herrnstein and Murray.

Fueling racism

Dennis M. Rutledge suggests that through soundbites of works like Jensen's famous study on the achievement gap, and Herrnstein and Murray's book The Bell Curve, the media "paints a picture of Blacks and other people of color as collective biological illiterates-- as not only intellectually unfit but evil and criminal as well." thus providing, he says "the logic and justification for those who would further disenfranchise and exclude racial and ethnic minorities." Many critics point out that 17 of the researchers whose work is referenced by the book are also contributors to Mankind Quarterly, a magazine with a slant towards racial eugenics. In his book The Bell Curve Wars: Race, Intelligence, and the Future of America Steven Fraser writes that by scrutinizing the footnotes and bibliography in The Bell Curve, readers can more easily recognize the project for what it is: a chilly synthesis of the work of disreputable race theorists and eccentric eugenicists. Since the book promulgated the idea that blacks were on average less intelligent than whites, some people fear that The Bell Curve can be used by extremists to justify genocide and hate crimes. 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.

Responses to criticisms

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. He also (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"). [13]

According to Christopher Chabirs, the most common responses to The Bell Curve involve "phony controversies". Chabris writes that "the vast majority of those commenting on The Bell Curve" in books such as The Bell Curve Wars "have little or no scientific authority".

Author's follow-up

Relation between IQ and earnings in the U.S.

IQ	<75	75–90	90–110	110–125	>125
Age 18	2,000	5,000	8,000	8,000	3,000
Age 26	3,000	10,000	16,000	20,000	21,000
Age 32	5,000	12,400	20,000	27,000	36,000
Values are the average earnings (1993 US Dollars) of each IQ sub-population.

Murray responded to specific criticisms of the analysis of the practical importance of IQ compared to socio-economic status (Part II of The Bell Curve) in a 1998 book Income Inequality and IQ To circumvent criticisms surrounding their use of a statistical control for socioeconomic status (SES), Murray adopted a sibling design. Rather than statistically controlling for parental SES, Murray compared life outcome differences among full sibling pairs who met a number of criteria in which one member of the pair has an IQ in the "normal" range and the other siblings has an IQ in a higher or lower IQ category. According to Murray, this design controls for all aspects of family background (full siblings share the same family background, growing up together in the same home and the same community).

Comparison of The Bell Curve control for parental SES and the sibling fixed-effect model of IQ and Income Inequality for IQ regression

Indicator	Bell Curve control for parental SES	Sibling fixed-effect model
Annual earnings, year-round workers	5548	5317
Years of schooling	0.59	0.45
Attainment of BA	1.76	1.87
High-IQ occupation	1.39	1.72
Out of labor force 1+ month	-0.34	-0.3
Unemployed 1+ month	-0.52	-0.47

Relation between IQ and life outcomes in the U.S. among sibling pairs in a "Utopian" sample

IQ	<75	75–90	90–110	110–125	>125
Mean years of education	11.4 (10.9)	12.3 (11.9)	13.4 (13.2)	15.2 (15.0)	16.5 (16.5)
Percentage obtaining B.A.	1 (1)	4 (3)	19 (16)	57 (50)	80 (77)
Mean weeks worked	35.8 (30.7)	39.0 (36.5)	43.0 (41.8)	45.1 (45.2)	45.6 (45.4)
Mean earned income	11,000 (7,500)	16,000 (13,000)	23,000 (21,000)	27,000 (27,000)	38,000 (36,000)
Percentage with a spouse who has earned income	30 (27)	38 (39)	53 (54)	61 (59)	58 (58)
Mean earned family income	17,000 (12,000)	25,000 (23,400)	37,750 (37,000)	47,200 (45,000)	53,700 (53,000)
Percentage children born out of wedlock	49 (50)	33 (32)	14 (14)	6 (6)	3 (5)
Fertility to date	2.1 (2.3)	1.7 (1.9)	1.4 (1.6)	1.3 (1.4)	1.0 (1.0)
Mother's mean age at birth	24.4 (22.8)	24.5 (23.7)	26.0 (25.2)	27.4 (27.1)	29.0 (28.5)
Values are "Utopian sample" ("Full sample"). Earning values are the 1993 US Dollars.

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 ABC 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. [14]

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).[15]

References

• Gottfredson, Linda S.; "Mainstream Science on Intelligence". Published in The Wall Street Journal, December 13, 1994, and also in Intelligence, January-February 1997.
• Claude S. Fischer et al.; Inequality by Design: Cracking the Bell Curve Myth. Princeton University Press, 1996, ISBN 0-691-02898-2.
• Bernie Devlin et al.; Intelligence, Genes, and Success: Scientists Respond to The Bell Curve. Copernicus Books, 1997, ISBN 0-387-94986-0.

External links

• "The Inequality Taboo", Commentary Magazine. Murray's update on what's been found out about "intractable" differences in relation to sex and race since The Bell Curve was published.
• Interview with Charles Murray, co-author of the Bell Curve
• James Heckman's critique of Murray and Herrnstein's statistical techniques
• American Psychological Association 1996 statement on issues raised by The Bell Curve
• "Intelligence: Knowns and Unknowns" Full text of APA report, from a non-APA web site
• "The Heritability of IQ"; Nature, 1997 Jul 31;388(6641):468-71
• "Heritability Estimates Versus Large Environmental Effects: The IQ Paradox Resolved"; Psychological Review, 2001, Vol. 108, No. 2, 346?369
• "Upstream : Issues : Bell Curve" Large collection of reviews and reactions to The Bell Curve
• "Mainstream Science on Intelligence" The Wall street Journal, December 13, 1994, p. A18 PDF scan from Linda Gottfredson's home page.
• "Revisiting the Bell Curve" An article by Alan Reifman, which reviews pertinent research on the genetic contribution to intelligence, the relative contributions of intelligence and social factors to success in life, and the potential of educational experience to improve cognitive ability.

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.
• The Bell Curve Wars: Intelligence and the Future of America, Steven Frazer, editor
• Dr. Eric Alterman's Weblog on Mediamatters.org,The Bell Curveball Parts 1 through 3 by Eric Alterman
• The Bell Curve Fallacy - A layman's argument against the Bell Curve