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Significance of group IQ differences

 * See also: Practical importance of IQ

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. 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.

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.

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. 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. and 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. (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.

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, 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%.

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.

Controlling for IQ
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.

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.

For additional discussion of the effects of controlling for group differences on a variety of outcomes and groups, see, and.

Between nations


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. Another peer-reviewed paper, Intelligence, Human Capital, and Economic Growth: An Extreme-Bounds Analysis, finds a strong connection between intelligence and economic growth. 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.

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. However, these environmental differences may operate in part by selecting for higher levels of IQ

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. 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, even though affirmative action discriminates against Asians in the admissions process (relative to Whites as well as to other minorities) 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. 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. 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, raising further questions about the benefits of affirmative action programs based on race as well as stereotypes about the intellectual capacity of races. 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. 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.”

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. 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. 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.

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. In a separate study, East Asians demonstrated high visuospatial scores, but slightly above average, average or slightly below average verbal scores. 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. 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).