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- Main article: Race and intelligence
Race and intelligence research measures the gaps in cognitive ability scores between different races or ethnicities and seeks to find the cause of these gaps. Average test scores vary based on several factors in addition to race, such as the method and setting used to test intelligence, the health and economic situation of the test takers, the presence of stereotype threat, and the period in history when the test was performed.  Some studies find that gaps in test scores are closing, while other studies find that the gaps are not.
Some explanations for the causes of the gaps suggest cultural factors, health, testing situations, stereotype threat, and other environmental factors. Some researchers have found evidence that genetics plays a large role in performance on intelligence tests.[attribution needed][How to reference and link to summary or text]Template:POV-statement Most researchers suspect that both genetics and environment play a role in determining intelligence test scores. In the past, disparities in performance were regarded as genetic.[How to reference and link to summary or text] Today , many psychologists remain undecided. Based on a survey conducted by Snyderman and Rothman (1998) the most common view among "intelligence experts" is that the Black-White IQ gap is caused by both genetic and environmental factors.
- 1 Explanations
- 2 Test data
- 3 Interpretations of measured group IQ differences
- 4 References
Explanations[edit | edit source]
- Main article: Race and intelligence (Explanations)
Although, most intelligence researchers believe that IQ differences among individuals reflect the general intelligence factor, g. the question of whether IQ differences among groups are substantially genetic remains unsettled. Researchers, such as Richard E. Nisbett caution that the studies that are most directly relevant to the question of whether the Black/White IQ gap is genetic in origin provide no evidence for a correlation between IQ and African (rather than European) ancestry. The best modern studies, says Nisbett indicate little relation between skin color and IQ. One modern study of blood types weakly suggests African superiority; the other two suggest no difference between the races.
According to the American Psychological Association, the difference between the average IQ scores of Blacks and Whites in the U.S. cannot be attributed to any obvious biases in test construction or cultural biases, though, it is clear, they say, that these differences, are well within the range of effect sizes that can be produced by environmental factors.
Although IQ differences between individuals is highly heritable, this does not mean that average IQ differences between racial groups are necessarily genetic in origin, because estimates of heritability depend on the range of environments tested. High heritability by itself is not informative about group differences, so any inferences made from within group heritability will depend on additional considerations. However, many scholars agree that no considerations of heritabilty are sufficient if group differences are caused by environmental factors that uniquely and uniformly affect all members of one group but not another.
Environmental explanations[edit | edit source]
Regarding the IQ gaps in the U.S., there are numerous possible explanations beside genetics. One author lists more than a hundred. It has been suggested that African-American culture disfavors academic achievement and fosters an environment that is damaging to IQ. Likewise, it is argued that the persistence of negative racial stereotypes reinforces this effect. Dr. John Ogbu writes that the condition of being a "caste-like minority" affects motivation and achievement, depressing IQ.
Arguing that IQ tests are often wrongly described as measuring "innate" rather than developed ability, Jencks and Phillips 1998 conclude that this "labeling bias" causes people to inappropriately attribute the Black-White gap to "innate" differences. They assert that non-cultural environmental factors cause gaps measured by the tests, rather than any possible innate difference based on genetics, and to use these tests as a measure of innate difference is misleading and improper.
Estimates of the significance of genetics vs. environment are dependent on the strength of environmental factors. For example, schizophrenia, regarded as highly heritable, has seen increased rates in second and third generation immigrants to Western European countries which do not seem to be the result of increased genetic susceptibility, but another, as yet unidentified, environmental factor(s) that seems to have become more influential.
Culture[edit | edit source]
Many anthropologists[attribution needed] have argued that intelligence is a cultural category; some cultures emphasize speed and competition more than others, for example. Speculations about innate differences in intelligence between ethnic groups have occurred throughout history. Aristotle in the 4th century B.C. and Cicero in the 1st. century B.C. disparaged the intelligence of the northern Europeans of the time, as did the Moors in Iberia in the 11th century.
Ogbu elaborates on this idea suggesting that African American popular culture serves to disengage students from academic achievement by proving the wrong kind of role models.
"What amazed me is that these kids who come from homes of doctors and lawyers are not thinking like their parents; they don't know how their parents made it," Professor Ogbu said in an interview. "They are looking at rappers in ghettos as their role models, they are looking at entertainers. The parents work two jobs, three jobs, to give their children everything, but they are not guiding their children."
The effort gap[edit | edit source]
Researchers Stephan Thernstrom and John Ogbu have suggested that black students perform poorly in part due to simple lack of effort. Stephan Thernstrom studied different kinds of schools and concluded that, while many environmental factors play a role in the achievement gap, a strong commitment to education was an essential element for academic success. Ogbu found that the black students were quite open in telling the researchers that, in general, their white classmates studied more, worked harder and cared more about getting good grades.
"In spite of the fact that the students knew and asserted that one had to work hard to succeed in Shaker schools, black students did not generally work hard. In fact, most appeared to be characterized by the low-effort syndrome ... (They) were not highly engaged in their schoolwork and homework." --John Ogbu
Pidgin language barriers[edit | edit source]
- See also: African American Vernacular English
Sandra Lee McKay author of Sociolinguistics and Language Teaching writes that language may present a barrier for students who speak pidgin and creole languages. Unlike other languages such as Spanish and Chinese, pidgin and creole languages such as African American Vernacular English (AAVE) are not commonly recognized in classroom settings. As a result of this, students are not taught the Standard American English (SAE) used on tests as a second language in the same way as students who speak Spanish or Chinese. Students who speak AAVE face challenges similar to those learning English as a Second Language. (ESL)
John Russel Rickford author of Unequal partnership: Sociolinguistics and the African American speech community rebutts misconceptions about the cognitive limitations of the use of AAVE notes the unfair disadvantages IQ tests pose for its speakers. Geneva Smitherman writes that "80 to 90 percent of American blacks” speak AAVE “at least some of the time". The preponderance of code-switching indicates that AAVE and SAE are met with different reactions or discernments. AAVE is often perceived by members of mainstream American society as indicative of low intelligence or limited education.
The effects of test construction on minority groups, such as the use of standard English, were examined by the 1996 APA report, which wrote that "controlled studies have shown, however, that none of them contributes substantially to the Black/White differential under discussion here (Jensen, 1980; Reynolds 82 Brown, 1984; for a different view see Helms, 1992). Moreover, efforts to devise reliable and valid tests that would minimize disadvantages of this kind have been unsuccessful." However the language gap still presents a barrier to education through adverse impacts in classroom settings where the need to teach English as a second language to students who come to school speaking AAVE is not commonly recognized.
Health[edit | edit source]
- Main article: Health and intelligence
In the developing world there are many factors can greatly decrease IQ scores. Examples include nutrition deficiencies in iodine and iron; certain diseases like malaria; unregulated toxic industrial substances like lead and mercury; and poor health care for pregnant women and infants. Also in the developed world there are many biological factors that can affect IQ. Increased rates of low birth weight babies and lower rates of breastfeeding in Blacks as compared to Whites are some factors of many that have been proposed to affect the IQ gap.
Exposure to violence[edit | edit source]
Exposure to violence in childhood has been associated with lower school grades. Recent research shows it may also have an impact on IQ. A group of largely African American urban first-grade children and their caregivers were evaluated using self-report, interview, and standardized tests, including IQ tests. The study found that exposure to violence and trauma-related distress in young children were associated with substantial decrements in IQ and reading achievement. Exposure to Violence or Trauma lead to a 7.5-point (SD, 0.5) decrement in IQ and a 9.8-point (SD, 0.66) decrement in reading achievement.Neighborhood risk has been related to lower school grades for African-American adolescents in another study from 2006.
The Flynn effect[edit | edit source]
- Main article: Flynn effect
The secular, international increase in test scores, commonly called the Flynn effect, is seen by Flynn and others as reason to expect the eventual convergence of average black and white IQ scores. Flynn argues that the average IQ scores in several countries have increased about 3 points per decade during the 20th century, which he and others attribute predominantly to environmental causes. This means, given the same test, the mean black American performance today could be higher than the mean white American performance in 1920, though the gains causing this appear to have occurred predominantly in the lower half of the IQ distribution. If changes in environment can cause changes in IQ over time, they argue, then contemporary differences between groups could also be due to an unknown environmental factor. On the supposition that the effect started earlier for whites, because their social and economical conditions began to improve earlier than did those of blacks, they anticipate that the IQ gap among races might change in the future or is even now changing. An added complication to this hypothesis is the question of whether the secular IQ gains can be predominantly a real change in cognitive ability. Flynn's face-value answer to this question is "No", and other researchers have found reason to concur. Responding to such concerns, Dickens and Flynn 2001 have proposed a solution which rests on genotype-environment correlation, hypothesizing that small initial differences in environment cause feedback effects which magnify into large IQ differences. Such differences would need to develop before age 3, when the black-white IQ gap can be first detected.
Stereotype threat[edit | edit source]
- Main article: Stereotype threat
Stereotype threat is the fear that one's behavior will confirm an existing stereotype of a group with which one identifies. This fear may in turn lead to an impairment of performance (Aronson, Wilson, & Akert, 2005). Stereotype threat was first articulated and documented by the social psychologists Claude Steele, Joshua Aronson, and Steven Spencer, who have conducted several studies on this topic.
"When capable black college students fail to perform as well as their white counterparts, the explanation often has less to do with preparation or ability than with the threat of stereotypes about their capacity to succeed."
- Claude M. Steele, The Atlantic Monthly, August 1999
Thin Ice: Stereotype Threat and Black College Students
It is suggested that reduced performance from "stereotype threat" could be a contributing factor to the gaps in IQ test scores. Steele and Aronson 1995 found that making race salient when taking a test of cognitive ability negatively affected high-ability African American students. Sackett et al. 2004 point out that these findings are widely misinterpreted to mean that eliminating stereotype threat eliminated the Black-White performance gap.
Other Factors[edit | edit source]
Many studies that attempt to test for heritability find results that do not support the genetic hypothesis. They include studies on IQ and skin color, self-reported European ancestry, children in post WWII Germany born to black and white American soldiers, blood groups, and mixed-race children born to either a black or a white mother. Many intervention and adoption studies also find results that do not support the genetic hypothesis. Non-hereditarians have argued that these are direct tests of the genetic hypothesis and of more value than indirect variables, such as skull size and reaction time. Hereditarians argue that these studies are flawed due to their age, lack of replication, problems with their sample population, or that they do in fact support the genetic hypothesis.
Fryer and Levitt 2006, with data from "the first large, nationally representative sample" of its kind, report finding only a very small racial difference when measuring mental function for children aged eight to twelve months, and that even these differences disappear when including a "limited set of controls". They argue that their report poses "a substantial challenge to the simplest, most direct, and most often articulated genetic stories regarding racial differences in mental function." They conclude that "to the extent that there are any genetically-driven racial differences in intelligence, these gaps must either emerge after the age of one, or operate along dimensions not captured by this early test of mental cognition."
Another recent theory hypothesizes that fluid cognition (gF') may be separable from general intelligence, and that gF' may be very susceptible to environmental factors, in particular early childhood stress. Some IQ tests, especially those used with children, are poor measures of gF', which means that the effect of the environment on intelligence regarding racial differences, the Flynn effect, early childhood intervention, and life outcomes may have been underestimated in many studies. The article has received numerous peer commentaries for and against.
Genetic explanation[edit | edit source]
- See also: Inheritance of intelligence
Arthur Jensen and others[attribution needed] have concluded that the US IQ gap is partially genetic. Rushton and Jensen say that while plausible environmental explanation for the lower mean IQ in Blacks in the U.S. can be offered in many cases, these explanations are less capable of explaining the higher average IQ of East Asians than Whites.
To support their theory, they often cite several arguments and observations:
- Black–White–East Asian differences in IQ, reaction time, and brain size are observed worldwide in a range of cultures and environments. In the United States, significant Black-White IQ differences are observable at every age above 3 years, within every occupation or socioeconomic level tested, in every region of the country, and at every time since the invention of ability tests.
- Jensen and others[attribution needed] have argued that the magnitude of race differences on different IQ subtests correlate with the extent to which those subtests measures g, which also correlates with measures of the subtests heritability. From these and other findings, they argue that race differences have a partly biological basis.
- The rising heritability of IQ with age (within all races; studies have found on average in the developed world heritability starts at 20% in infants, rises to 40% in middle childhood, and peaks at 80% in adulthood); and studies showing the virtual disappearance (~0.0) by adulthood of shared environmental effects on IQ (for example, family income, education, and home environment), with adopted siblings partaking in the studies no more similar in IQ than with strangers From these studies, they argue that most suggested environmental explanations for IQ difference between groups do not have a strong enough effect on IQ to fully account for group differences.
- Studies of US comparisons of both parents to children and siblings to each other finding regression to differing means for different races (85 for Blacks and 100 for Whites) across the entire range of IQs, despite the fact that siblings are matched for shared environment and genetic heritage, with regression unaffected by family socioeconomic status and generation examined
- Evidence against test construction and cultural bias: the internal consistency of item difficulty for all groups, the equivalent validity of tests in predicting academic and occupational outcomes for all groups, and the persistence of the IQ gap on relatively culture-free tests.
Other evidence, such as transracial adoption, certain racial admixture studies, behavior genetic modeling of group differences, "life-history" traits, and evolutionary explanations have also been proposed to indicate a genetic contribution to the IQ gaps and explain how these arose. Critics of this view, such as Robert Sternberg, argue that these studies are either flawed and thus inconclusive, or else that they support a primarily environment (<20% genetic) hypothesis. For example, Dolan and Hamaker 2001 argue that the statistical methods linking the Black-White gap to g are insufficient.
Test data[edit | edit source]
- Main article: Race and intelligence (test data)
The modern controversy surrounding intelligence and race 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. 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. Attempted world-wide compilations of average IQ by race generally place Ashkenazi Jews at the top, followed by East Asians and Whites, other Asians, Arabs, Blacks and Australian Aborigines. 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. Some reports indicate that the Black–White gap is smaller in the UK than in the U.S. Many studies also show large differences in IQ between different groups of Whites. For example, in Northern Ireland the IQ gap between Protestants and Catholics are as large as that between Blacks and Whites in the US. For example, in Israel, large gaps in test scores and achievement separate Ashkenazi Jews from other groups such as the Sephardi.
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). Measures of school achievement correlate fairly well with IQ, especially in younger children. In the United States, achievement tests find that by 12th grade Black students are performing on average only as well as White students in 10th grade, and Asian students in 8th grade; Hispanic students do only slightly better than Blacks. Whether the gaps are narrowing or not is debated.
Interpretations of measured group IQ differences[edit | edit source]
Given the observed differences in IQ scores between certain groups, a great deal of debate revolves around the significance of these observations. Some believe that these differences indicate a natural genetic hierarchy of races, with East Asians being the most genetically superior, Whites slightly below, and Blacks the most genetically inferior, and suggest that attempts to close the gaps are doomed to fail. Others believe that these differences are direct evidence of the social oppression of minority groups.
References[edit | edit source]
- Carraher, Carraher, and Schliemann (1985). studied a group of Brazilian street children. The investigation found that the same children who are able to do the mathematics needed to run their street businesses were often unable to do mathematics in a formal setting. See: Street Mathematics and School Mathematics By Terezinha Nunes, David William Carraher, Analucia Dias Schliemann ISBN 0521388139
- Olness, K. "Effects on brain development leading to cognitive impairment: a worldwide epidemic," Journal of Developmental and Behavioral Pediatrics 24, no. 2 (2003): 120–30.
- Black Americans reduce the racial IQ gap: Evidence from standardization samples William T. Dickens and James R. Flynn. Oct. 2006
- Ogbu JU (1978). Minority Education and Caste: The American System in Cross-Cultural Perspective. San Diego, CA: Academic Press. Cite error: Invalid
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- See Health and intelligence Cite error: Invalid
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- Claude M. Steele, The Atlantic Monthly, August 1999 Thin Ice: Stereotype Threat and Black College Students
- How Heritability Misleads about Race
- Gottfredson 2005b; Snyderman and Rothman 1987; Neisser et al. 1996; Gottfredson 1997a
- RACE, GENETICS, AND IQ, Richard E. Nisbett
- See for example APA's summary of their 1996 task force report (Neisser et al. 1996): "The differential between the mean intelligence test scores of Blacks and Whites does not result from any obvious biases in test construction and administration, nor does it simply reflect differences in socio-economic status" (Neisser et al. 1996); also: "It is clear, however, that these differences, whatever their origin, are well within the range of effect sizes that can be produced by environmental factors."(Neisser et al. 1996). The Gottfredson 1997a collective statement likewise states: "Intelligence tests are not culturally biased against American Blacks or other native-born, English-speaking people in the U.S. Rather, IQ scores predict equally accurately for all such Americans, regardless of race or social class."
- Herrnstein and Murray 1994, Murray 2005
- Jensen 1998
- Jensen 1998 refers to such environmental factors as "Factor X", a name which he also applies to environmentalist hypotheses about group differences that posit the existence of a "Factor X". If group differences were caused by racism, then racism would be a "Factor X". Rowe et al. 1994 and a number of subsequent studies sought and failed to find evidence for the existence of a Factor X. However, Gottfredson 2005 warns that these studies are not "well replicated".
- Boykin 1994
- Ogbu JU, Davis A (2003). Black American Students in an Affluent Suburb: A Study of Academic Disengagement. Lawrence Erlbaum Publishers. ISBN 0-8058-4515-1
- PBS Jencks Interview "If we change the names of the tests, they still measure the same thing but it wouldn't convey this idea that somehow you've gotten the potential of somebody when you measured their IQ. And I think that creates a big bias, because the people who do badly on the tests are labeled as people with low potential in many people's minds and they sometimes even believe that about themselves."
- Jencks and Phillips 1998 "... we find it hard to see how anyone reading these studies with an open mind could conclude that innate ability played a large role in the black-white gap."
- Relative risk for cognitive impairments in siblings of patients with schizophrenia. Biological Psychiatry, Volume 50, Issue 2, Pages 98-107 M. Egan
- Impaired attention, genetics, and the pathophysiology of schizophrenia.
- Aristotle: "Having spoken of the number of the citizens, we will proceed to speak of what should be their character. This is a subject which can be easily understood by any one who casts his eye on the more celebrated states of Hellas, and generally on the distribution of races in the habitable world. Those who live in a cold climate and in Europe are full of spirit, but wanting in intelligence and skill; and therefore they retain comparative freedom, but have no political organization, and are incapable of ruling over others. Whereas the natives of Asia are intelligent and inventive, but they are wanting in spirit, and therefore they are always in a state of subjection and slavery. But the Hellenic race, which is situated between them, is likewise intermediate in character, being high-spirited and also intelligent. Hence it continues free, and is the best-governed of any nation, and, if it could be formed into one state, would be able to rule the world." (Aristotle, Politics, ch. 7).
Cicero: "Do not obtain your slaves from Britain because they are so stupid and so utterly incapable of being taught that they are not fit to form a part of the household of Athens." Attributed to Cicero's Epistulae ad Atticum (Letters to Atticus), 68 BC-43 BC (latin text). Translation: Cicero 1918.
"Races north of the Pyrenees are of cold temperament and never reach maturity; they are of great stature and of a white colour. But they lack all sharpness of wit and penetration of intellect." Attributed to "Said of Toledo (a Moorish savant)" by Benedict 1999 (p.34), originally quoted in Hogben 1931.
- Why Are Black Students Lagging? By FELICIA R. LEE, The New York Times, November 30, 2002
- The academic gap may be an effort gap
- TOEFL to the Test: Are Monodialectal AAL-Speakes Similar to ESL Students?
- “Unequal partnership: Sociolinguistics and the African American speech community” John Russel Rickford. Language and Society 26/2 (1997), pp.161-97
- Geneva Smitherman, Talkin and Testifyin: The Language of Black America (Boston: Houghton Mifflin, 1977), 2.
- William Labov, Language in the Inner City: Studies in Black English Vernacular (Philadelphia: University of Pennsylvania Press, 1972).
- Intelligence: Knowns and Unknowns 
- American Shibboleth: Ebonics by Stanley M. (Ben) Novak
- Violence Exposure, Trauma, and IQ and/or Reading Deficits Among Urban Children Virginia Delaney-Black, MD, MPH; Chandice Covington, PhD, RN, CPNP; Steven J. Ondersma, PhD; Beth Nordstrom-Klee, PhD; Thomas Templin, PhD; Joel Ager, PhD; James Janisse, PhD; Robert J. Sokol, MD Vol. 156 No. 3, March 2002
- Family, peer, and neighborhood influences on academic achievement among African-American adolescents: One-year prospective effects
- Flynn 1987, Flynn 1987b, Flynn 1999, Flynn 1999b
- Colom et al. 2005
- Flynn 1999
- Wicherts et al. 2004 concluded that "the gains cannot be explained solely by increases at the level of the latent variables (common factors), which IQ tests purport to measure". An analysis by Rushton 1999 found that the IQ increases associated with the Flynn effect did not produce changes in g, which Rushton compares to the finding by Jensen 1998a that IQ increases associated with adoption likewise do not increase g. Flynn 1999b disagrees with Rushton's analysis.
- Rowe and Rodgers 2002 and others find this hypothesis unsupported by the available evidence. Dickens and Flynn 2002 respond to these criticisms.
- Rushton and Jensen 2005a
- The Effects of Stereotype Threat on the Standardized Test Performance of College Students J Aronson, CM Steele, MF Salinas, MJ Lustina - Readings About the Social Animal, 8th edition, E. Aronson
- See also Cohen and Sherman 2005, Helms 2005, Wicherts 2005 and Sackett et al. 2005 for discussion of the implications of stereotype threat for race and intelligence research.
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- Shuey 1966 reported the average correlation between skin color and IQ among American blacks is .1; for comparison Parra 2004 found the correlation between skin color and fraction of West-African ancestry is .4.
- Jenkins 1936
- Eyferth 1961; see note below
- Scarr et al. 1977, Loehlin et al. 1973
- Willerman et al. 1974
- Nisbett 2005
- Nisbett 2005
- Rushton and Jensen 2005b argue that these studies are "peculiarly old, the mean year of publication being 1960" and "actually very weak and nondecisive, not having been replicated even once". Jensen 1998b, for example, points out that while the study of children born in post-WWII Germany finds no difference between white and interracial children, it does find a large difference in IQ between boys and girls, suggesting that sampling artifacts have affected the results.
- Fryer and Levitt 2006 Testing for Racial Differences in the Mental Ability of Young Children "On tests of intelligence, Blacks systematically score worse than Whites, whereas Asians frequently outperform Whites. Some have argued that genetic differences across races account for the gap. Using a newly available nationally representative data set that includes a test of mental function for children aged eight to twelve months, we find only minor racial differences in test outcomes (0.06 standard deviation units in the raw data) between Blacks and Whites that disappear with the inclusion of a limited set of controls. The only statistically significant racial difference is that Asian children score slightly worse than those of other races. To the extent that there are any genetically-driven racial differences in intelligence, these gaps must either emerge after the age of one, or operate along dimensions not captured by this early test of mental cognition."
- How similar are fluid cognition and general intelligence? A developmental neuroscience perspective on fluid cognition as an aspect of human cognitive ability, Behavioral and Brain Sciences (2006), 29: 109-125 Cambridge University Press, Clancy Blair. Multiple comments can be seen on Google Scholar.
- Jensen 1998b
- For example, see Rushton and Jensen 2003; see also Spearman's hypothesis
- for example, inbreeding depression scores measured in Japan predict the magnitude of the Black-White gap in the United States. (Rushton 1989a)
- reviewed by Jensen 1998b
- Plomin et al. 2001
- for example, the children of wealthy, high IQ Black parents score lower than the children of poor, low IQ White parents (Jensen 1998b, p. 358); and for Black and White children with an IQ of 120, the siblings of the Black children average an IQ of 100 whereas the siblings of the White children average an IQ of 110; in comparison, for Black and White children with an IQ of 70, the siblings of the Black children average an IQ of 78 whereas the siblings of the White children average an IQ of 85 (Jensen 1973, pp. 107–119))
- Jensen 1980
- Rushton and Jensen 2005a, cited in "Black-White-East Asian IQ differences at least 50% genetic, scientists conclude in major law journal", and Murray 2005
- Reviewed by Rushton and Jensen 2005.
- For example: Nisbett 2005, Suzuki and Aronson 2005, Sternberg 2005, Dickens 2005
- Dolan and Hamaker 2001 reanalyzed the data from several earlier studies and concluded that Spearman's hypothesis is not an "empirically established fact" (i.e., that Black-White IQ differences may be due to differences in common factors other than g) due to insufficient power in the data to choose between alternative models. "This leaves the validity of Spearman's hypothesis, considered a central justification for the genetic explanation, an unresolved question." However, they did confirm that the Black-White IQ gap is not due to measurement artifacts, and is instead due to some measured factor that varies both within and between groups.
- Average IQ score plotted for each group. The normalization average of 100 is shown as a dotted line. Dozens of individual studies are represented. Data taken from review by Lynn 2006.
- Average IQ score and year of publication are plotted for each group. The normalization average of 100 is shown as a dotted line. Dozens of individual studies are represented. Data taken from review by Lynn 2006.
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