Race and intelligence (Average gaps among races)

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Main article: Race and intelligence
Approximate cumulative IQ distributions in the U.S. based on Wechsler Adult Intelligence Scale IQs for Whites (mean = 101.4, SD = 14.7) and Blacks (mean = 86.9, SD = 13.0) from (Reynolds, Chastain, Kaufman, & McLean, 1987, p. 330); distributions for Hispanics (mean = 91) and Asians (mean = 106) are less precise. Most reports estimate that the average IQ of Ashkenazi Jews (not shown) is greater than any other group (mean = 113).

The modern controversy surrounding race and intelligence focuses on the results of IQ studies conducted during the second half of the 20th century, mainly in the United States and some other industrialized nations. IQ studies outside these nations are few and small. It is uncertain what the average IQ or subgroup IQ tests scores would be with more complete studies in the developing world. IQ test scores in the developing world may be affected by factors less important in the developed world such as nutritional deficiencies. Most of the remainder of this article refers to studies attempting to explain race differences in IQ test scores in the US, and does not refer to the world as a whole.

IQ test score gap in the US

In almost every testing situation where tests were administered and evaluated correctly, a difference of approximately one standard deviation was observed in the US between the mean IQ score of Blacks and Whites. In the United States, the mean IQ score among Blacks is approximately 85 and the mean IQ score among Whites is approximately 100; the mean IQ score of Hispanics is usually reported to be between the mean Black and White scores (Herrnstein and Murray report a mean "Latino" IQ of 89 in The Bell Curve). The mean score for people of East Asian and Jewish descent is usually higher than the mean score of Whites, but the extent of that difference is not precisely known. However, several studies place the median IQ of Ashkenazi Jews (who make up the overwhelming majority of American Jews) at approximately one standard deviation above the mean for other Whites, with the primary Jewish advantage in verbal reasoning and the East Asian advantage primarily in spatial reasoning. In The Bell Curve, Herrnstein and Murray report mean IQ scores for East Asians and Jewish Americans of 106 and 113 (on a scale where Whites = 103), respectively.

2003 SAT by race-ethnicity.png
2003 SAT results by race/ethnicity. Redrawn from College Board statistics. College Board classifications are not homogeneous; for example, "Asian" includes East Asians and South Asians; "White" includes Jewish Americans and other Whites.
GRE by race.png
2001-2002 GRE results by race/ethnicity. Source: [3], Table A.2
Distribution of SAT scores by race-ethnicity.gif
Distribution of SAT math scores by race and ethnicity. [4]
Students who scored 600 or more on the math SAT.gif
Percentage of race/ethnic groups that scored above 600 on the math SAT [5]

Similar gaps are seen in other tests of cognitive ability or aptitude, including university admission exams such as the SAT and GRE as well as employment tests for corporate settings and the military (Roth et al. 2001).

School achievement gap

Main article: Achievement gap

Measures of school achievement correlate fairly well with IQ (uncorrected correlations are highest for younger children because of restricted ranges of IQ at higher educational levels). The National Assessment of Educational Progress in the United States, find that by 12th grade Black students are performing on average only as well as White and Asian students in 8th grade; Hispanic students do only slightly better than Blacks. Closing this achievement gap is one of the aims of the No Child Left Behind act in the United States. The gap has been attributed to academic disengagement of Black students and parents[1] and to environmental causes.[2] The school achievement gap can potentially be explained by many environmental factors that do not affect IQ tests to a similar degree, like bias in those giving grades or constructing tests.

Attempts to redress the achievement gap in the U.S. include Head Start and related early intervention programs. Neither Head Start nor most other (more intensive) programs have been able to produce lasting gains in IQ or school achievement.[3] Gains are lost after the programs end. Supporters note that they continue as long as the programs continue. The Abecedarian Early Intervention Project is an exception to this pattern, producing an IQ boost of approximately 5 points into adulthood.[9] Lack of sufficient funding is often cited as a reason for the failure of Head Start programs to have lasting impact.

Selected IQ data
Test Black-White gap (SD) White mean Black mean N Age Year Reference
Overall g 1.10 - - 6,246,729 Adults Various Roth, Bevier, Bobko et al. (2001)
AFQT '79 1.21 ? ? ? Adults 1979 reported in Herrnstein and Murray (1994)
AFQT '97 0.97 ? ? ? Adults 1997 reported in Murray (2005)
WAIS R 1.01 101.4 86.5 1,880 Adults 1981 Reynolds et al (1987)
WAIS III ? ? ? ? Adults 1997 ?
WJ 1.05 ? ? ? Adults & Children 2001 reported in Murray (2005); Schrank, F.A., K.S. McGrew, and R.W. Woodcock. 2001. Technical Abstract (Woodcock-Johnson III Assessment Service Bulletin No. 2). Itasca, IL: Riverside Publishing.
WJ 0.99 ? ? ? Children 2001 reported in Murray (2005); Schrank, F.A., K.S. McGrew, and R.W. Woodcock. 2001. Technical Abstract (Woodcock-Johnson III Assessment Service Bulletin No. 2). Itasca, IL: Riverside Publishing.
WISC IV 0.78 103.2 91.7 1,745 Children 2003 Prifitera, A., L.G. Weiss, D.H. Saklofske, et al. 2005. "The WISC-IV in the clinical assessment context." Pp. 3–32 in WISC-IV Clinical Use and Interpretation: Scientist-Practitioner Perspectives, edited by A. Prifitera, D. H. Saklofske, and L. G. Weiss.

Is the gap closing?

Long term White-Black gap in NAEP math scores [6]
Long term White-Black gap in NAEP reading scores [7]

Richard Nisbett and others[4] have argued that the Black-White gap on various ability tests has narrowed from the 1970s to the 1990s, including the Equality of Educational Opportunity (EEO) survey, the National Longitudinal Study, the High School and Beyond survey, the National Education Longitudinal Study, and the National Assessment of Educational Progress program (NAEP). The Journal of Blacks in Higher Education found that although the Black-White gap on the SAT declined from 1976-1988, it has been increasing since 1988. On the other hand, some studies find that the gap has been decreasing for most of the 20th century and that this trend continued during the nineties.[5]

Jensen[6] has argued that the Black-White differences in g have not narrowed. In support of this claim, he presents evidence that, while there have been gains in measures of acquired competency such as scholastic achievement, these improvements do not indicate gains in g. Jensen also argues that Black-White differences in g seen in measures of reaction time have not narrowed. A large meta-analysis using 6,246,729 samples found a mean Black-White score difference of 1.1 standard deviations (ranging from 0.38 to 1.46 depending on the g loading of the test). As to whether the IQ gap is narrowing, the authors speculated that any reduction was "either small, potentially a function of sampling error ... or nonexistent for highly g loaded" tests.[7] Gottfredson [8] agreed that the Black-White gap observed in the National Assessment of Educational Progress test has narrowed from 1.07 to 0.89 standard deviations. However, she then argues that reduction stopped by the mid-1980s and is compatible with stable group differences in g.

A large (21,260 children) and probably the most recent (1998) study found that the Black-White gap for young children in reading and math scores was much smaller than in earlier studies, and that all of the remaining difference could be explained by a few environmental factors.[9] One possible explanation is that the Flynn effect started earlier for Whites but has now stopped, while continuing for Blacks. Reading and math scores are correlated with, but not substitutable for, IQ, so these findings alone may not indicate convergence in the IQ gap. Still, the correlation of IQ with grades is highest in elementary school (0.6 to 0.7; Jensen 1998b), so convergence in scores may, in fact, indicate that the IQ gap is narrowing.

IQ gaps in other nations

Commonly cited IQ figures
for various groups
Group IQ avg Citation
Jewish Americans 113 Herrnstein & Murray (1994)
East Asians 106 Herrnstein & Murray (1994)
Lynn (1991a)
Whites 100 Herrnstein & Murray (1994)
Lynn (1991a)
Hispanics 89 Herrnstein & Murray (1994)
Native Americans 89 Lynn (1991a)
African Americans 85 Herrnstein & Murray (1994)
Lynn (1991a)
Roth et al. (2001)
Subsaharan Africans 70 Lynn (1991a)

Attempted compilations of average IQ by race generally place Ashkenazi Jews and East Asians on top, followed by non-Ashkenazi Whites, other Asians, Arabs, Blacks and Indigenous Australians. [10] See IQ and the Wealth of Nations for an attempted compilation of average IQ for different nations and a discussion of associated measurement problems.

The IQ scores vary greatly among different nations for the same group. Blacks in Africa score much lower than Blacks in the US. Studies on African Blacks have yielded results of 65 [11] and 69.[12] Lynn (1991a) suggests this value should be rounded up to 70. The book IQ and the Wealth of Nations gives values for African nations ranging from 59 for Equatorial Guinea to 77 for Zambia.

Studies on Native Americans yield results ranging from 70 to 90. Lynn (1991a) suggests that the mean of several studies, 89, may be a reasonable approximation. Native Americans score higher on tests of spatial than verbal reasoning, a trait also shared with East Asians.

Some reports indicate that the Black–White gap is smaller in the UK than in the U.S.[13] Other examples are Jews who score much lower in developing nations and Koreans who score much lower in Japan. There are also other examples of IQ score differences between close neighbors in the same nation, for example between French vs. Flemish speakers in Belgium, Slovaks vs. Gypsies in Slovakia, Irish and Scottish vs. English in Great Britain, and white speakers of Afrikaans vs. white speakers of English in South Africa. In Mexico, Whites score higher than Mestizos, who score higher than Native Mexican Indians. [14]

There has been at least one comparative study on IQ scores in different European nations. The difference between the highest and lowest average national IQ scores is 8 points. There is a not statistically significant correlation between the country's latitude and its average IQ score. Also, Southern Europeans have a larger variation than Northern Europeans. Norwegians have less than half of the variability of Whites in the US while Italians and Bulgarians have about 150%.[15]

In Israel, there is a large gap in test scores and achievement between the Ashkenazi Jews and other groups such as the Sephardi.[16] Gaps are seen between Israeli Jews and Ethiopian Jewish immigrants. [17] A similar gap in IQ scores and achievement is seen between the Chinese and Malays in Singapore.[18]

Both Lynn and Rushton have suggested that high IQ is associated with colder climates. To test this hypothesis, Templer and Arikawa (in press [doi:10.1016/j.intell.2005.04.002]; see discussion [10]) compare the national IQ data from Lynn and Vanhanen with data sets that describe national average skin color and average winter and summer temperatures. They find that the strongest correlations to national IQ were −0.92 for skin color and −0.76 for average high winter temperature. They interpret this finding as strong support for IQ-climate association. Other studies using different data sets find no correlation [11][12].

World-wide scores

Cognitive ability scores for the ten global genetic clusters identified in previous genetic cluster analysis[19] have been surveyed by Richard Lynn.[20] Lynn regards these ten population groups as races, and extracts racial averages from 620 published studies surveying a total of 813,778 tested individuals. When taken as individual national averages, the data available, particularly regarding the developing world, is speculative due to limited sampling, year of testing, and varying type of cognitive ability test used. Lynn's previous work, including the trade book IQ and the Wealth of Nations with Tatu Vanhanen, have received widespread and strong criticism for both bias and error.[21]

In general, Lynn lists East Asians and Europeans as demonstrating the highest average IQ, indigenous Americans and other Eurasians with intermediate average IQ, and Africans and Australian Aborigines with the lowest average IQ. According to Lynn, when the studies are grouped and taken as averages for the ten racial groups, the argument for their reliability is that, though additional evidence may be required to confirm some of the more limited estimates, many have very high reliability in the sense that different studies give similar results, as well as that they correlate highly with performance in international studies of achievement in mathematics and science and with national economic development.[22] Lynn argues established environmental hypotheses can explain a substantial amount of these differences. The data set for sub-Saharan Africans around the world, the one most often criticized, is drawn from 155 different studies with a combined sample of 387,286 people. 57 of the studies are from countries in Africa, 54 from western countries, and 16 from non-western countries outside of Africa.[23]

Some Ashkenazi Jews score significantly higher than any other group.[24] An IQ of 70 is often associated with mental retardation, but deficits in adaptive behavior, such as telling the time, interacting socially, and looking after oneself, have only limited correlation with IQ, and are more important than IQ in determining whether a person is able to live an independent life.[25]

IQ scores vary greatly among different nations for related groups. Blacks in Africa score much lower than Blacks in the US. Some reports indicate that the Black–White gap is smaller in the UK than in the U.S.[26] American Blacks average about 7-20% European admixture;[27] UK admixtures are not as well-studied. Many studies also show differences in IQ between different groups of Whites. In Israel, large gaps in test scores and achievement separate Ashkenazi Jews from other groups such as the Sephardi.[28]

From Lynn (in press)
Population IQ Majority Population Minority Population Total Population
# Studies # Countries # Studies # Countries # Studies # Countries Sample
East Asian 105 59 5 42 7 101 12 128,322
European 99 93 36 6 6 112 42 175,950
—N America 100
—NC & E Europe 99
—Portugal 97
—SE Europe 92
Arctic 91 15 2 15 2 2,690
Southeast Asian 87 11 6 7 3 13,433
Pacific Islander 29 10 7,729
—Maori 90 15 1
—Non-Maori 85 14 9
Amerindian 86 11 5 21 2 63 7 37,304
West/South Asian 84 37 15 61 9 98 24 65,855
—Near East 89
—India 82
Sub-Saharan Africa 115 28 387,286
—Africa 67 57 18
—Non-Western 71 14 6 2 1
—Western 85 54 3
—Khosian 54 3 1
Australoid 62 24 1 5 1 29 2 4,785
World 90 620 100 813,778

IQ and Retardation

The low average IQ of Blacks in Sub-Saharan Africa is often met with incredulity. Among whites, almost everyone with an IQ of 75 is also retarded, but among groups with lower average IQs this association no longer holds. The reason is that mental retardation describes both an inability to solve problems (what IQ measures) and an inability to perform everyday tasks (e.g. daily living skills, communication skills, and social skills). Many whites with very low IQ have a genetic disorder (e.g., Down syndrome), whereas that level of reasoning ability is nearer to the average for sub-Saharan Africans. Jensen (1998) describes this phenomenon at length, including his great surprise at finding that people with normal social skills can perform so poorly on tests of fluid reasoning.

An IQ of 70 is often associated with mental retardation, but deficits in adaptive behavior, such as telling the time, interacting socially, and looking after oneself, have only limited correlation with IQ, and are more important than IQ in determining whether a person is able to live an independent life (Mackintosh 1998, p. 177). Mercer 1973 reported that on the basis of IQ alone 10 times as many Blacks as Whites would be classified as retarded, but when adaptive behavior measures are added to the criterion, this difference completely disappears. Some ethnic differences in cognitive ability appear in some aspects of cognitive ability and not others (see below; Mackintosh 1998, p. 178). The Black-White disparity seen in IQ does not appear in some basic cognitive functions that don't involve more than minimal elaboration, transformation, or other mental manipulation (Mackintosh 1998, p. 178; Jensen 1973).

Hybrid vigor

Intelligence is associated with the degree of "hybrid vigor" (heterosis) manifested by offspring of cross-ethnic matings. Children of Japanese–Caucasian cross-ethnic matings score .26 SD higher on several cognitive tests than those from within-ethnic matings, despite having virtually identical parental educational and occupational backgrounds.[29] The increase in scores tends to be higher on cognitive tests that are more g-loaded, suggesting that hybrid vigor improves g. Heterosis may be partially responsible for the Flynn effect.[30]

Reaction time

In 1991, Richard Lynn tested 1,468 9-year old children consisting of Blacks from South Africa, East Asians from Hong Kong and Japan, and Whites from Britain and Ireland. The content of the tests involved flipping a switch after one or more lights came on. Lynn found that the decision times (the time taken to make a decision about what to do) had a low correlation with IQ data on Raven's Progressive Matrices tests also administered during the same study, and that movement times (the time taken to execute the decision) did not show any correlation. He found that the Asians had the fastest decision times, followed by the Whites, and then by the Blacks. He also determined that the Black children had movement times that were substantially faster than those of Whites and Asians on certain tests.[31] Studies have shown similar patterns in response time on tests of arithmetic [32] and international studies confirm the trend.[33]

Jensen (1993) has stated that this allows for an extension of Spearman's hypothesis to include reaction time. Based on these results, they have concluded that the observed East Asian-White-Black differences have a neurological basis.

Inspection times correlate with IQ by about .30 to .50 (Grudnik and Kranzler 2001).

Brain size & structure

see also Craniometry, Neuroscience and intelligence
Mean cranial capacity (cc)
Measurement East Asian European African
Autopsy 1351 1356 1223
Endocranial volume 1415 1362 1268
External head measurements 1335 1341 1284
Corrected for body size 1356 1329 1294
Mean 1364 1347 1267
Redrawn from Jensen 1998b, Table 12.1

Some historical and modern studies, using skull and head measurements, weighing of brains at autopsy, or more recently, magnetic resonance imaging, report racial differences in average brain size similar to those for IQ.[34] Other studies have not found these results. [citation needed] These studies are usually accompanied by a great deal of controversy.

Old studies

Several studies from the 19th century and early 20th century found racial differences. Some showed that whites had the largest measurements, which was the expected view at the time. This is different from more recent results [13][14](Rushton, 1991, 2000). As noted later, brain size and shape has changed greatly in the last century.

Morton drawing.png
Samuel George Morton's drawing of Black, White, and East Asian (Mongol) skulls [8]

[How to reference and link to summary or text] In his 1839 Crania Americana, anthropologist Samuel George Morton reported that the mean cranial capacity of the skulls of Whites was 87 in³ (1426cm³), while that of Blacks was 78 in³ (1278cm³). Based on the measurement of 144 skulls of Native Americans, he reported a figure of 82in³ (1344cm³).

Morton's work has been criticized by Stephen Jay Gould, who alleged in his 1981 book The Mismeasure of Man that Morton was guilty of fudging data and "overpacking" the skulls with filler. Despite Gould's retabulation of Morton's data, however, the differences in brain size among different races still persist, with the data still showing a difference of about four cubic inches between modern Caucasians and Africans. Gould writes that the differences are "trivial", but current head of the controversial Pioneer Fund J. Philippe Rushton (1996) responds that a difference of only a single cubic inch equates to millions of neurons. In 1988, J. S. Michael remeasured a random sample of Morton's skulls and concluded that Morton had made very few errors. J. Philippe Rushton (1989) additionally reanalyzed Gould's retabulation, concluding that Morton had shown a pattern of decreasing brain size proceeding from East Asians, Europeans, and Africans.

Cortical neurons (billions)
East Asian European African
13.767 13.665 13.185
Source: Rushton 2000

In 1873, Paul Broca found the same pattern by weighing brains at autopsy. Other historical studies showing a Black-White difference in brain size include Bean 1906, Mall 1909, Pearl 1934 and Vint 1934. In 1888, H.D. Rolleston reported that the brain of the Australian Aborigine weighed less than the brain of Blacks (44.3 oz, 1256 g) , which in turn weighed less than the brain of Whites (49 oz, 1389 g). He also found that the Australian brain was less convoluted than those of Whites (p. 33).

Some 19th century studies have also found that the brains of Whites are more convoluted than those of Blacks [15][16] or Australian Aborigines (Rolleston 1888, p. 33). It is often assumed that convolutions are associated with increased intelligence because they allow a greater surface area to be packed into a smaller volume. However, dolphins, who have shown no signs of super-human intelligence, have more convoluted brains than do humans (Ridgway, S.H. (1986). Dolphin brain size. p. 59-70 In: M.M. Bryden and R.J. Harrison (Eds) Research on Dolphins. Clarendon Press, Oxford. 478 pp.).

Recent studies

Cranial capacity-IQ.png
Relationship between group IQ and cranial capacity. Redrawn from Jensen 1998b, Fig. 12.4

In his controversial 1995 work Race, Evolution, and Behavior, J. Philippe Rushton reported an average endocranial volume of 1,415 cm³ for "Orientals [sic]", 1,362 for Whites, and 1,268 for Blacks. When adjusted for average body size, the differences become more pronounced; i.e., the encephalization quotients (EQ) display greater differences than do absolute brain sizes (Jerison 1973, Jerison 2000; Rushton 1991). Rushton 1991 found an EQ of 7.26 for East Asians as compared to 6.76 for Caucasians. Differences in brain size between Asians and Europeans sometimes do not appear until adjusted for body size (Rushton 1997). In some cases Europeans averaged higher absolute brain sizes than East Asians but lower relative brain sizes when adjusted for body size. [35]

Ulric Neisser, who co-authored the American Psychological Association's Task Force Report on Intelligence, examined Lynn and Rushton's data and writes, "although those studies exhibit many internal inconsistencies (and the within-groups variabilites are always much larger than the between-groups differences), there is indeed a small overall trend in the direction they describe." [36]

Findings of Ho et al (1980, Table 1). Left to right: Brain weight distributions for 222 Black females (μ=1158, σ=119), 395 White females (μ=1252, σ=125), 228 Black males (μ=1286, σ=138), and 416 White males (μ=1392, σ=130).

One other study showing similar patterns in average brain weight is Ho et al. 1980 which analyzed autopsy records from Case Western Reserve University (N=1,261) to determine the effects of age, gender, and race on brain weight. The authors found that while there was a large amount of overlap among the groups, there were also statistically significant differences between the groups, and found that White males had the largest brain weight, followed by Black males, White females, and Black females. For a discussion of gender differences in brain size see sex and intelligence. Ho et al. 1980 also discovered that mean brain mass decreased over a five year period fastest for White males, followed by Black males, White females, and Black females.

Other studies have shown the same pattern in average head size, including Rushton 1992, Rushton 1994, and the National Collaborative Perinatal Project [37] (described by Broman et al. 1987) which collected anthropometric data, including head measurements and IQ, on approximately 35,000 children from 1959 to 1974 (although the study began with over 50,000 subjects, some attrition occurred as with many longitudinal studies). Analyses of the data found the East Asian ? White ? Black pattern in head size and IQ at 4 months, 1 year, and 7 years of age.

Distribution of skull distance measurements for various racial groups. (F=Frontal skull distance measurement, O=Occipital skull distance measurement. From McShane 1983

East Asian brains have greater width and breadth (i.e., are more brachycephalic) and are more spherically shaped than those of Europeans, which are more so than those of Africans. Africans tend to have longer and narrower (more dolichocephalic) brains. [38] Beals et al. proposed that the longer and narrower African brain evolved for better heat dissipation in a warmer climate, while East Asians and Europeans evolved comparatively shorter and wider brains for thermoregulatory purposes in a cooler climate. Rushton and Ankney 2000 (pp. 612-613) question the thermoregulatory hypothesis, instead positing that brachycephalization and sphericalization allow for greater brain size. At the same time, Rushton and Ankney believe it is possible that the need to thermoregulate in Africa may have selected against increasing brain size. Rushton and Ankney 2000 found a pattern of descending prognathism, glabella size, postorbital constriction, and temporal fossae in African, European, and East Asian skulls and propose that these structures shrank over the course of evolution to allow greater brain size.

Rushton has been accused by other researchers of misrepresenting the data. When they have reanalyzed the data, Zack Cernovsky et al. argue that many of Rushton's claims are incorrect. [17]

Extensive statistical analyses by Beals et al. showed that cranial size varies primarily with climatic zones (e.g.,distance from the equator), not race. According to Beals et al., the correlations of brain size to race are spurious: smaller crania are found in warmer climates, irrespective of race. Several other studies found that North American Blacks were superior to American Whites in brain weight, that they had cranial capacities that compared favorably to the average for various samples of Caucasians, and that they had excess neurons larger than many groups of Caucasoids, for example, the English and the French. In general, skulls from people in countries with poverty and infant malnutrition are smaller regardless of race. [18]

Modern studies using MRI imaging shows a weak to moderate correlation between brain size and IQ [39] and have shown that brain size correlates with IQ by a factor of approximately .40 among adults.[40] The correlation between brain size and IQ seems to hold for comparisons between and within families.[41] although one study found no correlation within family.[42] A study on twins[43] showed that frontal gray matter volume was correlated with g and highly heritable. A related study has reported that the correlation between brain size (reported to have a heritability of 0.85) and g is 0.4, and that correlation is mediated entirely by genetic factors.[44] Note that none of the MRI studies have studied racial differences.

In a 2005 review of the literature [19], Rushton and Jensen claim that MRI studies show racial differences in brain size. The cited study (Harvey et al. 1994) compared brain size between a group of 26 persons with bipolar disorder and a group of 48 persons with schizophrenia and also included 34 healthy controls. The distribution of age and race was approximately equal across the three groups and consisted of Caucasians, Blacks, and West Indians (p. 692, table 1). Harvey et al. write,

Over the entire sample intracranial volume was related to height (P=0.0001), gender (P=0.001), ethnicity (P=0.007), and IQ (P=0.03), but not age; larger volumes generally occurred in those subjects who were taller, male, and Caucasian" (p. 693).

(Note that East Asians were not included in the study, that there was a sex ratio imbalance among the schizophrenic group (p. 692), that intracranial volume is not the same thing as brain size, and that the sample where most have serious mental disease may not be representative for population as a whole.)

Cranial vault size and shape have changed greatly during the last 150 years in the US. These changes must occur by early childhood because of the early development of the vault. The explanation for these changes may be related to the Flynn effect.[45]


  1. Ogbu 2003
  2. Thernstrom and Thernstrom 2003
  3. Jensen (1998)
  4. Grissmer 1994; Grissmer et al. 1998a; Grissmer et al. 1998b; Hedges and Nowell 1998; Nisbett 1995, Nisbett 1998, Nisbett 2005
  5. Min-Hsiung Huang and Robert M. Hauser, "Convergent Trends in Black-White Test-Score Differentials in the U.S.: A Correction of Richard Lynn1," University of Wisconsin–Madison, July 31, 2000.
  6. Jensen 1998, pp. 375-376, 407-408, 494-495
  7. Roth et al. 2001
  8. Gottfredson (2005)
  9. Roland G. Fryer Jr. and Steven D. Levitt, "Understanding the Black-White Test Score Gap in the First Two Years of School," The Review of Economics and Statistics 86, no. 2 (2004).
  10. For examples, see Herrnstein and Murray 1994; Lynn 1991a
  11. Fick, cited in Lynn, 1991a; Lynn and Holmshaw 1990
  12. Owen, cited in Lynn, 1991a
  13. IQ comments, Gene Expression, September 23, 2003.
  14. Lynn, Backhoff, and Contreras (2005)
  15. Buj (1981). Some of the data can be found on-line on a web page about Greek IQ.
  16. Willms and Chen 1989
  17. Kaniel and Fisherman 1991
  18. Lynn 1977a
  19. Cavalli-Sforza et al. 1994
  20. Lynn 2006
  21. Sociologist Thomas Volken argues the data for national IQs is "highly deficient," citing limited sampling and varying tests and years (Volken). In a review of The Bell Curve, Leon Kamin writes that "Lynn's distortions and misrepresentations of the data constitute a truly venomous racism, combined with scandalous disregard for scientific objectivity."(Kamin 1995) In contrast to Kamin's strongly worded attack on Lynn, W. D. Hamilton described Lynn in a review of another of Lynn's books as doing "an excellent job with the facts" and being "brave [and] thick-skinned ... to swim against ... popular antirealistic currents."[1] Examples of problematic national IQ figures include that the stated average IQ score of 59 for Equatorial Guinea is based on one test of 48 children aged 10-14 in 1984; the Ethiopian average is derived from a study of Ethiopians who immigrated to Israel a year prior, and whose low scores were thought by the original authors to be a reflection of temporary adjustment to a different culture and language (note that this data is not used in the averages presented below). Kamin also argued Lynn selectively excluded data showing a similar score in Whites and sub-Saharan Africans: "Lynn chose to ignore the substance of Crawford-Nutt's paper, which reported that 228 black high school students in Soweto scored an average of 45 correct responses on the Matrices--HIGHER than the mean of 44 achieved by the same-age white sample on whom the test's norms had been established and well above the mean of Owen's coloured pupils." (Kamin 1995)
  22. Rushton 2005
  23. Malloy 2006 [2]
  24. Lynn estimates United States and British Ashkenazim IQ scores of 107-115, in contrast to average IQ of Ashkenazim in Israel at 103. He suggests this estimate may be lower due to selective migration effects in relation to the U.S. and Britain, and immigrants from the former Soviet Block countries having posed as Ashkenazim.
  25. (Mackintosh 1998, p. 177). Mercer 1973 reported that on the basis of IQ alone 10 times as many Blacks as Whites would be classified as retarded, but when adaptive behavior measures are added to the criterion, this difference completely disappears. Some ethnic differences in cognitive ability appear in some aspects of cognitive ability and not others (see below; Mackintosh 1998, p. 178). The Black-White disparity seen in IQ does not appear in some basic cognitive functions that don't involve more than minimal elaboration, transformation, or other mental manipulation (Mackintosh 1998, p. 178; Jensen 1973).
  26. Gene Expression 2003
  27. Burchard et al. 2003;Parra et al. 1998
  28. Willms and Chen 1989
  29. Nagoshi and Johnson 1986, p. 204
  30. Mingroni 2004
  31. Richard Lynn, "Race Differences in Intelligence: A Global Perspective," The Mankind Quarterly 31, no. 3 (1991): 255–96; Means for Progressive Matrices and 12 reaction time measures for 9-year-old children from five countries.
  32. Jensen 1993; Jensen and Whang 1994.
  33. See Lynn and Shigehisa 1991 for Japan; Chan and Lynn (1989) for Hong Kong and Britain; Lynn (1991) for Ireland; and Lynn and Holmshaw 1990 for South Africa.
  34. Jensen 1998b, pp. 436-443. For individual studies, see Ho et al. 1980a, Ho et al. 1980b; Harvey_et_al. 1994; Rushton 1991.
  35. Rushton 1994
  36. Neisser 1997, p. 80
  37. Missing note.
  38. Beals et al. 1984; McShane 1983; Rushton and Ankney 2000
  39. Harvey, Persaud, Ron, Baker, & Murray, 1994
  40. McDaniel 2005
  41. Gignac et al. 2003; Jensen 1994; Jensen and Johnson 1994.
  42. Schoenemann et al. 2000
  43. Thompson et al. 2001
  44. Posthuma et al. 2002
  45. Gravlee et al. 2003a; Gravlee et al. 2003b; Jantz and Jantz 2000; Jantz 2001


Main article: Race and intelligence (References)

Race and intelligence

Research: Test data, Explanations, and Interpretations
Controversies: Utility and Potential for bias
History | Media portrayal | References

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