Spearman's hypothesis
Encyclopedia
Spearman's hypothesis states that the magnitude of the black-white difference in tests of cognitive ability is entirely or mainly a function of the extent to which a test measures general mental ability, or g. The hypothesis, first formalized by Arthur Jensen
in the 1980s based on Charles Spearman
's earlier comments on the topic, argues that differences in g are the sole or major source of differences between blacks and whites observed in many studies of race and intelligence
. Jensen devised the method of correlated vectors to study the hypothesis. This, and a similar relationship regarding the degree of heritability
of tests and the magnitude of black-white differences on tests, have been argued to support the partially-genetic explanation for black-white average IQ differences.
Various criticisms have been advanced and the validity of the arguments remain unresolved.
Based on Spearman's insight, Arthur Jensen set out to formalize and test the hypothesis in the 1980s. He argued that the correlations between the g-loadings of various tests and the magnitude of the black-white gap on them would provide strong evidence for the validity of the hypothesis. He proposed strong and weak forms of the hypothesis, with the former stating that differences in g are the sole cause of the gap, and the latter stating that g is the main cause of the gap. In order to test this, he developed the method of correlated vectors, and, in a series of studies, demonstrated that the correlations obtained (+0.6, on average) supported the weak form of the hypothesis. However, Jensen has argued that the correlations would be substantially higher if certain corrections for statistical artifacts were made.
Closely related to Spearman's hypothesis is the relationship between how high heritability
a test has and how large the racial gaps are for that test. The degree of heritability can be estimated by, for example, examining how much inbreeding depression
from cousin marriage
s affect a test or how much siblings differ from one another on a test. The method of correlated vectors can be used to compare the degree of heritability and magnitude of racial gaps for several tests. Rushton
and Jensen argued that the results were similar as to those found when examining the relationship between degree of g-loading and magnitude of racial gaps. This also occurs across nations. The effect of inbreeding depression on different tests calculated from cousin marriages in Japan
predicted the magnitudes of black-white IQ gaps on different tests in the United States
.
Jensen has argued that if Spearman's hypothesis is proven correct, it would, at least partially, answer the question why the black-white gap varies across different IQ tests. Moreover, it would prove that the main source of the differences between whites and blacks in IQ tests is the same as the main source of differences between individuals within each racial group, namely g. This would suggest that to understand the nature of the black-white gap, one would have to understand the nature of g. In 2002, Jensen stated that he had now tested Spearman's hypothesis on 25 large independent samples, and it had been confirmed on every one. Based on all these studies, he asserted, "the overall probability that Spearman's hypothesis is false is less than one in a billion."
Rushton and Jensen argue that a test's g-loading also correlates with scholastic and workplace performance, heritability estimates determined from twin studies
, inbreeding depression scores calculated in children of cousin-marriages, brain evoked potential
s, brain pH
levels, brain glucose
metabolism, as well as nerve conduction velocity, reaction time, and other physiological factors. This, they argue, support the view that g is biological and heritable. Therefore, the supposed confirmation of Spearman's hypothesis, and the similar relationship for heritability, support, they argue, the theory that average racial IQ differences are partially genetic.
. Flynn
earlier argued that the most g-loaded and heritable tests are those that have seen the highest increases due to the Flynn effect. Using Jensen's argument this could then be taken as evidence that the Flynn effect is substantially due to genetic causes, which is absurd. Rushton and Jensen have argued that a more complete analysis shows that higher g-loading or heritabiliy are either unrelated to the Flynn effect or are negatively related with relatively smaller increases for such tests. Flynn in a 2010 reply stated regarding his earlier argument that "Today I would not be surprised or disturbed if a wider array of evidence negated this result" but that this is irrelevant since the basic assumption, that confirmation of Spearman's hypothesis would support the partially-genetic theory, is basically flawed (as explained in a later section).
has argued that positive correlations predicted by Spearman's hypothesis are likely only psychometric artefacts which also arise with measures which have nothing to do with 'general ability', for example, the number of toys and books a child has. He claims that these positive correlations will arise with any set of moderately correlated random data, once the sample is split into high and low groups. According to Dolan and Lubke, Schönemann's analysis is incorrect. Using simulations, they show that the correlations are not positive by mathematical necessity.
Dolan and Hamaker in 2001 reanalyzed the data from a previous study that had used the statistical method invented by Jensen (the method of correlated vectors) with a more recent and improved method (multigroup confirmatory factor analysis). They argue that the method of correlated vectors is dependent on the existence of g and if more complex models are used the results are unclear. As such, "we cannot accept Spearman's hypothesis as an 'empirically established fact".
Rushton and Jensen (2010) argued that this criticism misses the point because there was no absolute claim that g had been proven—only that the results were what would have been expected if a g did in fact exist. Furthermore, several more recent studies using multigroup confirmatory factor analysis have supported Spearman's hypothesis in the US and South Africa for black-white IQ gaps and in Serbia for Romani
-white IQ gaps. They also argue that the heritability of a test correlates with the g-load of the test which support the existence of a genetic g.
They further summarize criticisms of this position:
Nisbett writes that the argument is based mainly on the g-loadings for the subtests of the WISC
. With the exception of one subtest the differences in g-loading are very small. Furthermore, the argument is based on crystallized
g. If instead looking at fluid g, then the subtests with the highest g-loading are the ones which have increased the most due to the Flynn effect. This, argues Nisbett, argues against high g-loading being due to genetics. Even if using crystallized g, then blacks have gained almost as much on a highly crystallized g-loaded test as on IQ tests in general, which contradicts what the hereditarians would predict, that blacks would gain much less on highly g-loaded tests.
Rushton and Jensen have disputed this and argue in a response to Nisbett that a more complete analysis show consistent results for black-white differences on the Flynn effect and g-loadings supporting a genetic role.
Flynn (2010) has criticized the basic assumption that confirmation of Spearman's hypothesis would support the partially-genetic explanation for black-white average IQ differences. He argued that also only environmental causes for average group IQ differences would cause the differences to be greater for more complex tasks. Using the example of basketball
, he argued that the differences between two unequally trained groups would be less for skills involving less complexity, such as layup
s, than they would be for more complex skills such as long-distance jump shot
s. Furthermore, he argued that complex tasks tend to be more affected by genetic differences in inherited traits and therefore have higher heritability. Thus, also only environmentally caused group differences would cause the gaps to be larger for more heritable tasks.
Arthur Jensen
Arthur Robert Jensen is a Professor Emeritus of educational psychology at the University of California, Berkeley. Jensen is known for his work in psychometrics and differential psychology, which is concerned with how and why individuals differ behaviorally from one another.He is a major proponent...
in the 1980s based on Charles Spearman
Charles Spearman
Charles Edward Spearman, FRS was an English psychologist known for work in statistics, as a pioneer of factor analysis, and for Spearman's rank correlation coefficient...
's earlier comments on the topic, argues that differences in g are the sole or major source of differences between blacks and whites observed in many studies of race and intelligence
Race and intelligence
The connection between race and intelligence has been a subject of debate in both popular science and academic research since the inception of intelligence testing in the early 20th century...
. Jensen devised the method of correlated vectors to study the hypothesis. This, and a similar relationship regarding the degree of heritability
Heritability
The Heritability of a population is the proportion of observable differences between individuals that is due to genetic differences. Factors including genetics, environment and random chance can all contribute to the variation between individuals in their observable characteristics...
of tests and the magnitude of black-white differences on tests, have been argued to support the partially-genetic explanation for black-white average IQ differences.
Various criticisms have been advanced and the validity of the arguments remain unresolved.
Spearman's hypothesis and inbreeding depression
In his 1927 book The Abilities of Man, Charles Spearman discussed briefly the results of an American study where a sample of white and black schoolchildren were given a diverse battery of mental tests. There was a gap favoring whites in all tests, but its magnitude varied considerably across the tests. Spearman noted that the gap was at its largest in tests thought to be particularly good measures of g.Based on Spearman's insight, Arthur Jensen set out to formalize and test the hypothesis in the 1980s. He argued that the correlations between the g-loadings of various tests and the magnitude of the black-white gap on them would provide strong evidence for the validity of the hypothesis. He proposed strong and weak forms of the hypothesis, with the former stating that differences in g are the sole cause of the gap, and the latter stating that g is the main cause of the gap. In order to test this, he developed the method of correlated vectors, and, in a series of studies, demonstrated that the correlations obtained (+0.6, on average) supported the weak form of the hypothesis. However, Jensen has argued that the correlations would be substantially higher if certain corrections for statistical artifacts were made.
Closely related to Spearman's hypothesis is the relationship between how high heritability
Heritability
The Heritability of a population is the proportion of observable differences between individuals that is due to genetic differences. Factors including genetics, environment and random chance can all contribute to the variation between individuals in their observable characteristics...
a test has and how large the racial gaps are for that test. The degree of heritability can be estimated by, for example, examining how much inbreeding depression
Inbreeding depression
Inbreeding depression is the reduced fitness in a given population as a result of breeding of related individuals. It is often the result of a population bottleneck...
from cousin marriage
Cousin marriage
Cousin marriage is marriage between two cousins. In various jurisdictions and cultures, such marriages range from being considered ideal and actively encouraged, to being uncommon but still legal, to being seen as incest and legally prohibited....
s affect a test or how much siblings differ from one another on a test. The method of correlated vectors can be used to compare the degree of heritability and magnitude of racial gaps for several tests. Rushton
J. Philippe Rushton
Jean Philippe Rushton is a Canadian psychology professor at the University of Western Ontario who is most widely known for his work on racial group differences, such as research on race and intelligence, race and crime, and the application of r/K selection theory to humans in his book Race,...
and Jensen argued that the results were similar as to those found when examining the relationship between degree of g-loading and magnitude of racial gaps. This also occurs across nations. The effect of inbreeding depression on different tests calculated from cousin marriages in Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
predicted the magnitudes of black-white IQ gaps on different tests in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
.
Jensen has argued that if Spearman's hypothesis is proven correct, it would, at least partially, answer the question why the black-white gap varies across different IQ tests. Moreover, it would prove that the main source of the differences between whites and blacks in IQ tests is the same as the main source of differences between individuals within each racial group, namely g. This would suggest that to understand the nature of the black-white gap, one would have to understand the nature of g. In 2002, Jensen stated that he had now tested Spearman's hypothesis on 25 large independent samples, and it had been confirmed on every one. Based on all these studies, he asserted, "the overall probability that Spearman's hypothesis is false is less than one in a billion."
Rushton and Jensen argue that a test's g-loading also correlates with scholastic and workplace performance, heritability estimates determined from twin studies
Twin study
Twin studies help disentangle the relative importance of environmental and genetic influences on individual traits and behaviors. Twin research is considered a key tool in behavioral genetics and related fields...
, inbreeding depression scores calculated in children of cousin-marriages, brain evoked potential
Evoked potential
An evoked potential is an electrical potential recorded from the nervous system of a human or other animal following presentation of a stimulus, as distinct from spontaneous potentials as detected by electroencephalography or electromyography .Evoked potential amplitudes tend to be low, ranging...
s, brain pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
levels, brain glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
metabolism, as well as nerve conduction velocity, reaction time, and other physiological factors. This, they argue, support the view that g is biological and heritable. Therefore, the supposed confirmation of Spearman's hypothesis, and the similar relationship for heritability, support, they argue, the theory that average racial IQ differences are partially genetic.
The Flynn effect
One criticism of Spearman's hypothesis has concerned the Flynn effectFlynn effect
The Flynn effect is the name given to a substantial and long-sustained increase in intelligence test scores measured in many parts of the world. When intelligence quotient tests are initially standardized using a sample of test-takers, by convention the average of the test results is set to 100...
. Flynn
James R. Flynn
James Robert Flynn PhD FRSNZ , aka Jim Flynn, Emeritus Professor of Political Studies at the University of Otago in Dunedin, New Zealand, researches intelligence and has become well known for his discovery of the Flynn effect, the continued year-after-year increase of IQ scores in all parts of the...
earlier argued that the most g-loaded and heritable tests are those that have seen the highest increases due to the Flynn effect. Using Jensen's argument this could then be taken as evidence that the Flynn effect is substantially due to genetic causes, which is absurd. Rushton and Jensen have argued that a more complete analysis shows that higher g-loading or heritabiliy are either unrelated to the Flynn effect or are negatively related with relatively smaller increases for such tests. Flynn in a 2010 reply stated regarding his earlier argument that "Today I would not be surprised or disturbed if a wider array of evidence negated this result" but that this is irrelevant since the basic assumption, that confirmation of Spearman's hypothesis would support the partially-genetic theory, is basically flawed (as explained in a later section).
The validity of g
Peter SchönemannPeter Schonemann
Peter H. Schönemann was a German born psychometrician and statistical expert. He was Professor Emeritus in the Department of Psychological Sciences at Purdue University. His research interests included multivariate statistics, multidimensional scaling and measurement, quantitative behavior...
has argued that positive correlations predicted by Spearman's hypothesis are likely only psychometric artefacts which also arise with measures which have nothing to do with 'general ability', for example, the number of toys and books a child has. He claims that these positive correlations will arise with any set of moderately correlated random data, once the sample is split into high and low groups. According to Dolan and Lubke, Schönemann's analysis is incorrect. Using simulations, they show that the correlations are not positive by mathematical necessity.
Dolan and Hamaker in 2001 reanalyzed the data from a previous study that had used the statistical method invented by Jensen (the method of correlated vectors) with a more recent and improved method (multigroup confirmatory factor analysis). They argue that the method of correlated vectors is dependent on the existence of g and if more complex models are used the results are unclear. As such, "we cannot accept Spearman's hypothesis as an 'empirically established fact".
Rushton and Jensen (2010) argued that this criticism misses the point because there was no absolute claim that g had been proven—only that the results were what would have been expected if a g did in fact exist. Furthermore, several more recent studies using multigroup confirmatory factor analysis have supported Spearman's hypothesis in the US and South Africa for black-white IQ gaps and in Serbia for Romani
Romani
Romani relates or may refer to:- Nationality :*The Romani people**their Romani language*The Latin term for the ancient Romans, see Roman citizenship*The Italian term for inhabitants of Rome...
-white IQ gaps. They also argue that the heritability of a test correlates with the g-load of the test which support the existence of a genetic g.
Criticism
Spearman's hypothesis is not without its critics. Psychologists Hunt and Carlson write:They further summarize criticisms of this position:
Nisbett writes that the argument is based mainly on the g-loadings for the subtests of the WISC
Wechsler Intelligence Scale for Children
The Wechsler Intelligence Scale for Children , developed by Dr. David Wechsler, is an individually administered intelligence test for children between the ages of 6 and 16 inclusive that can be completed without reading or writing...
. With the exception of one subtest the differences in g-loading are very small. Furthermore, the argument is based on crystallized
Fluid and crystallized intelligence
In psychology, fluid and crystallized intelligence are factors of general intelligence originally identified by Raymond Cattell...
g. If instead looking at fluid g, then the subtests with the highest g-loading are the ones which have increased the most due to the Flynn effect. This, argues Nisbett, argues against high g-loading being due to genetics. Even if using crystallized g, then blacks have gained almost as much on a highly crystallized g-loaded test as on IQ tests in general, which contradicts what the hereditarians would predict, that blacks would gain much less on highly g-loaded tests.
Rushton and Jensen have disputed this and argue in a response to Nisbett that a more complete analysis show consistent results for black-white differences on the Flynn effect and g-loadings supporting a genetic role.
Flynn (2010) has criticized the basic assumption that confirmation of Spearman's hypothesis would support the partially-genetic explanation for black-white average IQ differences. He argued that also only environmental causes for average group IQ differences would cause the differences to be greater for more complex tasks. Using the example of basketball
Basketball
Basketball is a team sport in which two teams of five players try to score points by throwing or "shooting" a ball through the top of a basketball hoop while following a set of rules...
, he argued that the differences between two unequally trained groups would be less for skills involving less complexity, such as layup
Layup
A layup in basketball is a two-point shot attempt made by leaping from below, laying the ball up near the basket, and using one hand to bounce it off the backboard and into the basket. The motion and one-handed reach distinguish it from a jump shot. The layup is considered the most basic shot in...
s, than they would be for more complex skills such as long-distance jump shot
Jump shot
In basketball , a jump shot is an attempt to score a basket by jumping, usually straight up, and in mid-jump, propelling the ball in an arc into the basket. It is accomplished by the player bringing his or her elbow up until it is aligned with the hoop, then sent towards the hoop in a high arc. It...
s. Furthermore, he argued that complex tasks tend to be more affected by genetic differences in inherited traits and therefore have higher heritability. Thus, also only environmentally caused group differences would cause the gaps to be larger for more heritable tasks.