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Significance of group IQ differences

See also: Practical importance of IQ

Within societies

Scope

The distribution of IQ scores among individuals of each race overlap substantially. In a random sample of equal numbers of US Blacks and Whites, Jensen estimates most variance in IQ would be unrelated to race or social class.^[1] The average IQ difference between two randomly paired people from the U.S. population is approximately 17 points, and this only increases to 20 points when the pair are black and white. When the pair are siblings, the average difference is still 12 points.^{[citation needed]}

In essays accompanying the publication of The Bell Curve, Herrnstein and Murray argue that whether the cause of the IQ gap is genetic or environmental does not really matter because that knowledge alone would not help to eliminate the gap and that knowledge should not impact the way that individuals treat one another. They argue that group differences in intelligence ought not to be treated as more important or threatening than individual differences, but suggest that one legacy of Black slavery has been to exacerbate race relations such that Blacks and Whites cannot be comfortable with group differences in IQ or any other traits.^[2]^[3]

Moreover, although it may appear paradoxical, it could be argued that an indirect outcome of social egalitarianism would be to raise the genetic contribution to intelligence to as high as possible, by minimizing environmental inequalities and any negatively IQ-impacting cultural and socio-economic differences.^[4] If all such inequalities could somehow be completely eliminated, any remaining group (but not individual) IQ differences would then be 100% hereditary: the only remaining factor that could potentially contribute to race-based outcome differences.

Practical importance

The appearance of a large practical importance for intelligence for some life outcomes makes some scholars claim that the source and meaning of the IQ gap is a pressing social concern.^[5] Gordon 1997 and Gottfredson 1997b argue that the IQ gap is reflected by gaps in the academic, economic, and social factors correlated with IQ. However, others dispute the general importance of the role of IQ for real-world outcomes, especially for differences in accumulated wealth and general economic inequality in a nation. One study found that wealth, race and schooling are important to the inheritance of economic status, but IQ is not a major contributor and the genetic transmission of IQ is even less important.^[6] (See "Practical importance of IQ".)

The effects of differences in mean IQ between groups (regardless if the cause is social or biological) are amplified by two statistical characteristics of IQ. First, there seem to be minimum statistical thresholds of IQ for many socially valued outcomes (for example, high school graduation and college admission). Second, because of the shape of the normal distribution, only about 16% of the population is at least one standard deviation above the mean. Thus, although the IQ distributions for Blacks and Whites are largely overlapping, different IQ thresholds can have a significant impact on the proportion of Blacks and Whites above and below a particular cut-off.

More information IQ range, Whites ...

**IQ Cohorts & Significance (U.S.)**
IQ range	Whites	Blacks	Black:White ratio	Training prospects	High school dropout	Lives in poverty	"Middle-Class Values" index^[7]
<75	3.6%	18.0%	~5:1	simple, supervised work; eligible for government assistance	55%	30%	16%
75-90	18.3%	41.4%	~2:1	very explicit hands on training; IQ >80 for military training; no government assistance	35%	16%	30%
90-100	24.3%	24.9%	~1:1	mastery learning, hands on	6%	6%	50%
100-110	25.9%	11.9%	~1:2	written material plus experience	6%	6%	50%
110-125	22.5%	3.6%	~1:6	college format	0.4%	3%	67%
>125	5.4%	0.2%	~1:32	independent, self-teaching	0%	2%	74%
Based on Wechsler Adult Intelligence Scale IQs for Whites (mean = 101.4, SD = 14.7) and for Blacks (mean = 86.9, SD = 13.0) from (Reynolds, Chastain, Kaufman, & McLean, 1987, p. 330). Training prospects from Wonderlic 1992 and Gottfredson 1997. Significance data is from Herrnstein and Murray 1994, and is based on Whites only. Results from the total population are nearly indistinguishable. Results for Blacks only are similar but not identical (see the table below for comparisons between groups). Note that these are merely correlations. For example, poverty could be both a cause and consequence of low IQ.

Small differences in IQ, while relatively unimportant at the level of an individual, could theoretically have large effects for the United States population as a whole. As a demonstration of these possible effects, Herrnstein and Murray 1994 used a resampling technique to argue that, all else equal, a simulated 3-point drop in average IQ had little effect on factors like marriage, divorce, or unemployment. However, their study found that a simulated drop in IQ from 100 to 97-points increased poverty rates by 11% and the proportion of children living in poverty by 13%. In the simulation, similar rises occurred in rates of children born to single mothers, men in jail, high school drop-out, and men prevented from working due to health-related problems. In contrast, when they simulated an increase in average IQ of 3-points to 103, they calculated that poverty rates fell 25%, children living in poverty fell 20%, and high school drop-out rates fell 28%.^[8]

Professors James Heckman and Nicholas Lemann, as well as several other scholars and scientists have the criticized validity and reliability of the data which led to the aforementioned findings by Herrnstein and Murray 1994.^[9]^[10]

Controlling for IQ

More information Condition (matching IQ), Black % ...

**Group Outcomes After Being Statistically Adjusted to Match IQ**
Condition (matching IQ)	Black %	Latino %	White %
High school graduation (103)	93	91	89
College graduation (114)	68	49	50
High-level occupation (117)	26	16	10
Living in poverty (100)	11	9	6
Unemployed for 1 month or more (100)	15	11	11
Married by age 30 (100)	58	75	79
Unwed mother with children (100)	51	17	10
Has ever been on welfare (100)	30	15	12
Mothers in poverty receiving welfare (100)	74	54	56
Having a low birth-weight baby (100)	6	5	3
Average annual wage (100)	$25,001	$25,159	$25,546
Men ever incarcerated (100)	5	3	2
"Middle-Class Values" index^[7] (100)	32	45	48
from Herrnstein & Murray (1994), Chapter 14. Professors James Heckman and Nicholas Lemann, as well as several other scholars and scientists have criticized the validity and reliability of the data which led to this chart.^[11]^[12]

Because IQ correlates with a number of social and economic outcomes that have been found to differ between the black and white populations overall, The Bell Curve argues that the disparities in outcomes are due to group differences in IQ (See above chart).Professors James Heckman and Nicholas Lemann and others claim that its findings are based on data that is not completely valid and reliable.^[13]^[14]

According to Murray and Herrnsteins' Bell Curve, when IQ is statistically controlled for, the probability of having a college degree or working in a high-IQ occupation is higher for Blacks than Whites. Controlling for IQ shrinks the income gap from thousands to a few hundred dollars. Controlling for IQ cuts differential poverty by about three-quarters and unemployment differences by half. However, controlling for IQ has little effect on differential marriage rates. For many other factors, controlling for IQ eliminates the differences between Whites and Hispanics, but the Black-White gap remains (albeit smaller).

White populations are not homogeneous groups regarding real-world outcomes. For example, in the U.S. 33.6% of persons with self-reported Scottish ancestry completed college, while only 16.7% of persons with self-reported French-Canadian ancestry have done so.^[15]

For additional discussion of the effects of controlling for group differences on a variety of outcomes and groups, see Nyborg and Jensen 2001, and Kanazawa 2005.

Between nations

Richard Lynn's early research on Japanese IQ initiated an academic controversy and became part of Western countries' surprise in the early 1980s at the Japanese' unexpected economic and industrial achievements. (*Discover* 1982)

Some people have attributed differential economic growth between nations to differences in the intelligence of their populations. One example is Richard Lynn's IQ and the Wealth of Nations. The book is sharply criticized in the peer-reviewed paper The Impact of National IQ on Income and Growth.^[16] Another peer-reviewed paper, Intelligence, Human Capital, and Economic Growth: An Extreme-Bounds Analysis, finds a strong connection between intelligence and economic growth.^[17] It has been argued that East Asian nations underachieve compared to IQ scores. One suggested explanation is that verbal IQ is more important than visuospatial IQ.^[18]

Jared Diamond's Guns, Germs and Steel instead argues that historical differences in economic and technological development for different areas can be explained by differences in geography (which affects factors like population density and spread of new technology) and differences in available crops and domesticatable animals.^[19] However, these environmental differences may operate in part by selecting for higher levels of IQ^[20]

For high-achieving minorities

The book World on Fire notes the existence in many nations of minorities that have created and control a disproportionate share of the economy, a market-dominant minority. Examples include Chinese in Southeast Asia; Indians in the United States and Britain; Whites, Indians, Lebanese and Igbo people of Western Africa; Whites in Latin America; and Jews in pre-World War II Europe, modern America, and modern Russia. These minorities are often resented and sometimes persecuted by the less successful majority.

In the United States, Jews, Asian Indians, Japanese, and Chinese earn incomes 1.72, 1.42, 1.32, and 1.12 times the American average, respectively.^[21] Jews and East Asians have higher rates of college attendance, greater educational attainment, and are many times overrepresented in the Ivy League and many of the United States' most prestigious schools,^[22] even though affirmative action discriminates against Asians in the admissions process (relative to Whites as well as to other minorities)^[23] At Harvard, for example, Asian American and Jewish students together make up 51% of the student body, though only constituting roughly 6% of the US population.^[24] In various Southeast Asian nations, Chinese control a majority of the wealth despite being a minority of the population and are resented by the majority, in some cases being the target of violence.^[25] Likewise, African immigrants to the US have the highest educational attainment rates of any immigrant group in the United States with higher levels of completion than the stereotyped Asian American model minority,^[26]^{[verification needed]} raising further questions about the benefits of affirmative action programs based on race as well as stereotypes about the intellectual capacity of races.^[27]^{[need quotation to verify]}Despite the ongoing controversy about IQ difference in the US. Gargi Bhattacharyya , Liz Ison and Maud Blair have found that IQ differences between black and white populations in the UK and elsewhere are virtually non-existent. In fact, Blacks of African descents in the UK, on average, earn more money and obtain higher levels of education than the native white populations.^[28] According to the London Daily Times “Black Africans have emerged as the most highly educated members of British society, surpassing even the Chinese as the most academically successful ethnic minority.”^[29]

More information Areas, U.S. Population ...

Areas	U.S. Population	All Immigrants	African Immigrants	Asian Americans	Europe, Russia & Canada	Latin, South America & Carribbean
Not Fluent in English	0.6%	30.5%	7.6%	23.4%	11.5%	44.0%
Less Than High School	17.1%	39.1%	12.1%	21.2%	23.5%	57.4%
College Degree	23.1%	23.3	43.8%	42.5%	28.9%	9.1%
Advanced Degree	2.6%	4.2	8.2%	6.8%	5.8%	1.9%

SOURCE: 2000 US CENSUS

Achievement in science, a high-complexity occupation in which practitioners tend to have IQs well above average, also appears consistent with some group IQ disparity.^[30] Only 0.25% of the world population is Jewish, but Jews make up an estimated 28% of Nobel prize winners in physics, chemistry, medicine, and economics.^[31] In the U.S., these numbers are 2% of the population and 40% of winners. Over half of the world chess champions from 1886 to 2000 had at least one Ashkenazi Jewish parent.^[32]

Some studies have shown significant variation in IQ subtest profiles between groups. In one analysis of IQ studies on Ashkenazi Jews, for example, high verbal and mathematical scores, but average or below average visuospatial scores were found.^[33] In a separate study, East Asians demonstrated high visuospatial scores, but slightly above average, average or slightly below average verbal scores.^[34] The professions in which these populations tend to be over-represented differ, and some believe the difference is directly related to IQ subtest score patterns asserted to exist.^[35] The high visiuospatial/average to below average verbal pattern of subtest scores has also been asserted to exist in fully assimilated third-generation Asian Americans, as well as in the Inuit and Native Americans (both of Asian origin).^[36]

[1]
Jensen, A. R. (1998). The g Factor: The Science of Mental Ability. Westport, CT: Praeger Publishers. ISBN 0-275-96103-6. p. 357. Equal-sized random samples of children from California schools were used for this analysis. Social class was rated on a ten-point scale based on parents' education and occupation. Only 30% of total variance in IQ is associated with differences between race and social class, whereas 65% exists within each racial and social class group. The single largest source of IQ variance exists between siblings within the same family.
[2]
Herrnstein, R. J. and Murray, C. (1994). The Bell Curve: Intelligence and Class Structure in American Life. New York: Free Press. ISBN 0-02-914673-9.
[3]
Charles Murray (September 2005). "The Inequality Taboo". Commentary Magazine 120 (2): 13-22.
[4]
The Blank Slate, pp. 106-107.^[who?]
[5]
Sackett et al. 2004: "Sub-group differences in performance on high-stakes tests represent one of American society's most pressing social problems, and mechanisms for reducing or eliminating differences are of enormous interest" (p.11).
[6]
Bowles and Gintis 2002.
[7]
The criteria for the "Middle-Class Values" index were: (for men) obtained high school degree (or more), were in labor force (but could be unemployed) throughout previous year (1989), never incarcerated, were still married to their first wife; (for women) obtained a high school degree, had never given birth out of wedlock, never incarcerated, were still marreid to their first husband. Individuals unable to work and those still in school were excluded from this analysis, as well as never-married individuals who satisfied all the other criteria. Poverty is not a criterion, nor is having children.
[8]
For this calculation, Herrnstein and Murray altered the mean IQ (100) of the U.S. National Longitudinal Survey of Youth's population sample by randomly deleting individuals below an IQ of 103 until the population mean reached 103. Their random deletion procedure was conducted twice and the calculated results were averaged together. Herrnstein and Murray note that their calculation ignore secondary effect. (Herrnstein_and_Murray 1994, pp. 364-368)
[9]
Cracked Bell by Professor James Heckman in Reason (March 1995).
[10]
The Bell Curve Flattened by Nicholas Lemann in Slate (January 1996).
[11]
Cracked Bell by Professor James Heckman in Reason (March 1995).
[12]
The Bell Curve Flattened by Nicholas Lemann in Slate (January 1996).
[13]
Cracked Bell by Professor James Heckman in Reason (March 1995).
[14]
The Bell Curve Flattened by Nicholas Lemann in Slate (January 1996).
[15]
These values were taken from Kangas 1999, which reprints U.S. Census data which was originally reported by Hacker 1995, p. 105. Drummond 2005 challenges the factual accuracy of other reporting by Kangas 1999.
[16]
Thomas Volken, "The Impact of National IQ on Income and Growth."
[17]
Jones and Schneider 2005
[18]
La Griffe du Lion 2004
[19]
Richard Nisbett argues in his 2004 The Geography of Thought that some of these regional differences shaped lasting cultural traits, such as the collectivism required by East Asian rice irrigation, compared with the individualism of ancient Greek herding, maritime mercantilism, and money crops wine and olive oil (pp. 34-35).
[20]
This theory is discussed by Jensen 1998b (pp. 435-437), Lynn 1991b and Rushton 2000 in general and by both Wade 2006 and Steve Sailer with respect to Guns, Germs, and Steel. See Race and intelligence (Explanations)#Rushton's application of r-K theory. .. Voight et al. 2006 state generally that "a number of recent studies have detected more signals of adaptation in non-African populations than in Africans, and some of those studies have conjectured that non-Africans might have experienced greater pressures to adapt to new environments than Africans have" (Kayser et al. 2003, Akey et al. 2004, Storz et al. 2004, Stajich and Hahn 2005, Carlson et al. 2005).
[21]
Sowell 1981, p. 5
[22]
Sowell 1981, pp. 7, 93
[23]
A study by Princeton researchers Espanshade and Chung 2005 analyzes the effects of admission preferences at elite universities in terms of SAT points (1600-point scale): Blacks +230; Hispanics +185; Asians -50; Recruited athletes +200; Legacies (children of alumni) +160. "Our results show that removing consideration of race would have a minimal effect on white applicants to elite universities. The number of accepted white students would increase by 2.4%." Asian percent of accepted students, in contrast, would increase by 33% (from 23.7% to 31.5%). "Nearly four out of every five places in the admitted class not taken by African-American and Hispanic students would be filled by Asians."
[24]
Hacker 2005
[25]
Sowell 1981, pp. 133-134; Purdey 2002
[26]
AsianNation.org data from [1-Percent Public Use Microdata Sample (PUMS) Files] US Census 2000
[27]
Top Colleges Take More Blacks, but Which Ones? The New York Times By SARA RIMER and KAREN W. ARENSON Published: June 24, 2004
[28]
Minority Ethnic Attainment and Participation in Education and Training: The Evidence (Bhattacharyya, Ilson, Blair, 2000)
[29]
London Daily Times (January, 23, 1994, as reported in Stringer and McKie 1997:190; Re-reported by Smedley in Lieberman 2001:p87)
[30]
Weyl 1969 and Weyl 1989, cited by Lynn 1991a.
[31]
jinfo.org 2004
[32]
Jewish World Chess Champions accessed December 30th, 2005.
[33]
Cochran et al. 2005, p. 4
[34]
Lynn, , Mackintosh 1998, p.178)
[35]
Lynn 1991a
[36]
Murray and Herrnstein 1994